Methods for targeted electrosurgery on contained herniated discs

ABSTRACT

Apparatus and methods for treating an intervertebral disc by ablation of disc tissue. A method of the invention includes positioning at least one active electrode within the intervertebral disc, and applying at least a first high frequency voltage between the active electrode(s) and one or more return electrode(s), wherein the volume of the nucleus pulposus is decreased, pressure exerted by the nucleus pulposus on the annulus fibrosus is reduced, and discogenic pain of a patient is alleviated. In other embodiments, a curved or steerable probe is guided to a specific target site within a disc to be treated, and the disc tissue at the target site is ablated by application of at least a first high frequency voltage between the active electrode(s) and one or more return electrode(s). A method of making an electrosurgical probe is also disclosed.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present invention is a continuation-in-part of PCTApplication No. 00/13706, filed May 17, 2000 (Attorney Docket No.S-5PC), which claims priority from U.S. patent application Ser. No.09/316,472, filed May 21, 1999 (Attorney Docket No. S-5), which is acontinuation-in-part of U.S. patent application Ser. No. 09/295,687,filed Apr. 21, 1999 (Attorney Docket No. E-7-2) and U.S. patentapplication Ser. Nos. 09/054,323 and 09/268,616, filed Apr. 2, 1998 andMar. 15, 1999, respectively (Attorney Docket Nos. E-5 and E-7-1,respectively), each of which are continuation-in-parts of U.S. patentapplication Ser. No. 08/990,374, filed Dec. 15, 1997 (Attorney DocketE-3), which is a continuation-in-part of U.S. patent application Ser.No. 08/485,219, filed on Jun. 7, 1995 (Attorney Docket 16238-000600),the complete disclosures of which are incorporated herein by referencefor all purposes. This application is also a continuation-in-part ofU.S. patent application Ser. No. 09/026,851, filed Feb. 20, 1999(Attorney Docket No. S-2), which is a continuation-in-part of U.S.patent application Ser. No. 08/690,159, filed Jul. 18, 1996 (AttorneyDocket No. 16238-001610), the complete disclosure of which isincorporated herein by reference for all purposes.

[0002] The present invention is related to commonly assigned co-pendingU.S. patent application Ser. No. 09/181,926, filed Oct. 28, 1998(Attorney Docket No. S-1-2), U.S. patent application Ser. No.09/130,804, filed Aug. 7, 1998 (Attorney Docket No. S-4), U.S. patentapplication Ser. No. 09/058,571, filed on Apr. 10, 1998 (Attorney DocketNo. CB-2), U.S. patent application Ser. No. 09/248,763, filed Feb. 12,1999 (Attorney Docket No. CB-7), U.S. patent application Ser. No.09/026,698, filed Feb. 20, 1998 (Attorney Docket No. S-3), U.S. patentapplication Ser. No. 09/074,020, filed on May 6, 1998 (Attorney DocketNo. E-6), U.S. patent application Ser. No. 09/010,382, filed Jan. 21,1998 (Attorney Docket A-6), U.S. patent application Ser. No. 09/032,375,filed Feb. 27, 1998 (Attorney Docket No. CB-3), U.S. patent applicationSer. Nos. 08/977,845, filed on Nov. 25, 1997 (Attorney Docket No. D-2),08/942,580, filed on Oct. 2, 1997 (Attorney Docket No. 16238-001300),U.S. patent application Ser. No. 08/753,227, filed on Nov. 22, 1996(Docket 16238-002200), U.S. patent application Ser. No. 08/687,792,filed on Jul. 18, 1996 (Docket No. 16238-001600), and PCT InternationalApplication, U.S. National Phase Serial No. PCT/US94/05168, filed on May10, 1994, now U.S. Pat. No. 5,697,909 (Attorney Docket 16238-000440),which was a continuation-in-part of U.S. patent application Ser. No.08/059,681, filed on May 10, 1993 (Attorney Docket 16238-000420), whichwas a continuation-in-part of U.S. patent application Ser. No.07/958,977, filed on Oct. 9, 1992 (Attorney Docket 16238-000410) whichwas a continuation-in-part of U.S. patent application Ser. No.07/817,575, filed on Jan. 7, 1992 (Attorney Docket 16238-00040), thecomplete disclosures of which are incorporated herein by reference forall purposes. The present invention is also related to commonly assignedU.S. Pat. No. 5,697,882, filed Nov. 22, 1995 (Attorney Docket16238-000700), the complete disclosure of which is incorporated hereinby reference for all purposes.

BACKGROUND OF THE INVENTION

[0003] The present invention relates to a medical apparatus having adistal curved configuration which avoids contact of the apparatus distalend with an introducer device. The present invention also relates to thefield of electrosurgery, and more particularly to surgical devices andmethods which employ high frequency electrical energy to treat tissue inregions of the spine. The present invention is particularly suited forthe treatment of the discs, cartilage, ligaments, and other tissuewithin the vertebral column.

[0004] The major causes of persistent, often disabling, back pain aredisruption of the disc annulus, chronic inflammation of the disc,herniation of the nucleus pulposus, or relative instability of thevertebral bodies surrounding a given disc, such as the instability thatoften occurs due to a stretching of the interspinous tissue surroundingthe vertebrae. Intervertebral discs mainly function to cushion andtether the vertebrae, while the interspinous tissue (i.e., tendons andcartilage, and the like) function to support the vertebrae so as toprovide flexibility and stability to the patient's spine.

[0005] Spinal discs comprise a central hydrophilic cushion, the nucleuspulposus, surrounded by a multi-layered fibrous ligament, the annulusfibrosus. As discs degenerate, they lose their water content and height,bringing the adjoining vertebrae closer together. This results in aweakening of the shock absorption properties of the disc and a narrowingof the nerve openings in the sides of the spine which may pinch thesenerves. This disc degeneration can eventually cause back and leg pain.Weakness in the annulus from degenerative discs or disc injury can allowfragments of nucleus pulposus from within the disc space to migratethrough the annulus fibrosus and into the spinal canal. There, displacednucleus or protrusion of annulus fibrosus, e.g., herniation, may impingeon spinal nerves. A weakening of the annulus fibrosus can cause the discto bulge, e.g., a contained herniation, and the mere proximity of thenucleus pulposus or the damaged annulus to a nerve can cause directpressure against the nerve, resulting in pain and sensory and motordeficit.

[0006] Often, inflammation from disc herniation can be treatedsuccessfully by non-surgical means, such as rest, therapeutic exercise,oral anti-inflammatory medications or epidural injection ofcorticosteroids. Such treatments result in a gradual but progressiveimprovement in symptoms and allows the patient to avoid surgicalintervention.

[0007] In some cases, the disc tissue is irreparably damaged, therebynecessitating removal of a portion of the disc or the entire disc toeliminate the source of inflammation and pressure. In more severe cases,the adjacent vertebral bodies must be stabilized following excision ofthe disc material to avoid recurrence of the disabling back pain. Oneapproach to stabilizing the vertebrae, termed spinal fusion, is toinsert an interbody graft or implant into the space vacated by thedegenerative disc. In this procedure, a small amount of bone may begrafted and packed into the implants. This allows the bone to growthrough and around the implant, fusing the vertebral bodies andpreventing reoccurrence of the symptoms.

[0008] Until recently, surgical spinal procedures resulted in majoroperations and traumatic dissection of muscle and bone removal or bonefusion. To overcome the disadvantages of traditional traumatic spinesurgery, minimally invasive spine surgery was developed. In endoscopicspinal procedures, the spinal canal is not violated and thereforeepidural bleeding with ensuing scarring is minimized or completelyavoided. In addition, the risk of instability from ligament and boneremoval is generally lower in endoscopic procedures than with openprocedure. Further, more rapid rehabilitation facilitates fasterrecovery and return to work.

[0009] Minimally invasive techniques for the treatment of spinaldiseases or disorders include chemonucleolysis, laser techniques, andmechanical techniques. These procedures generally require the surgeon toform a passage or operating corridor from the external surface of thepatient to the spinal disc(s) for passage of surgical instruments,implants and the like. Typically, the formation of this operatingcorridor requires the removal of soft tissue, muscle or other types oftissue depending on the procedure (i.e., laparascopic, thoracoscopic,arthroscopic, back, etc.). This tissue is usually removed withmechanical instruments, such as pituitary rongeurs, curettes, graspers,cutters, drills, microdebriders and the like. Unfortunately, thesemechanical instruments greatly lengthen and increase the complexity ofthe procedure. In addition, these instruments might sever blood vesselswithin this tissue, usually causing profuse bleeding that obstructs thesurgeon's view of the target site.

[0010] Once the operating corridor is established, the nerve root isretracted and a portion or all of the disc is removed with mechanicalinstruments, such as a pituitary rongeur. In addition to the aboveproblems with mechanical instruments, there are serious concerns becausethese instruments are not precise, and it is often difficult, during theprocedure, to differentiate between the target disc tissue, and otherstructures within the spine, such as bone, cartilage, ligaments, nervesand non-target tissue. Thus, the surgeon must be extremely careful tominimize damage to the cartilage and bone within the spine, and to avoiddamaging nerves, such as the spinal nerves and the dura matersurrounding the spinal cord.

[0011] Lasers were initially considered ideal for spine surgery becauselasers ablate or vaporize tissue with heat, which also acts to cauterizeand seal the small blood vessels in the tissue. Unfortunately, lasersare both expensive and somewhat tedious to use in these procedures.Another disadvantage with lasers is the difficulty in judging the depthof tissue ablation. Since the surgeon generally points and shoots thelaser without contacting the tissue, he or she does not receive anytactile feedback to judge how deeply the laser is cutting. Becausehealthy tissue, bones, ligaments and spinal nerves often lie withinclose proximity of the spinal disc, it is essential to maintain aminimum depth of tissue damage, which cannot always be ensured with alaser.

[0012] Monopolar and bipolar radiofrequency devices have been used inlimited roles in spine surgery, such as to cauterize severed vessels toimprove visualization. Monopolar devices, however, suffer from thedisadvantage that the electric current will flow through undefined pathsin the patient's body, thereby increasing the risk of undesirableelectrical stimulation to portions of the patient's body. In addition,since the defined path through the patient's body has a relatively highimpedance (because of the large distance or resistivity of the patient'sbody), large voltage differences must typically be applied between thereturn and active electrodes in order to generate a current suitable forablation or cutting of the target tissue. This current, however, mayinadvertently flow along body paths having less impedance than thedefined electrical path, which will substantially increase the currentflowing through these paths, possibly causing damage to or destroyingsurrounding tissue or neighboring peripheral nerves.

[0013] Other disadvantages of conventional RF devices, particularlymonopolar devices, is nerve stimulation and interference with nervemonitoring equipment in the operating room. In addition, these devicestypically operate by creating a voltage difference between the activeelectrode and the target tissue, causing an electrical arc to formacross the physical gap between the electrode and tissue. At the pointof contact of the electric arcs with tissue, rapid tissue heating occursdue to high current density between the electrode and tissue. This highcurrent density causes cellular fluids to rapidly vaporize into steam,thereby producing a “cutting effect” along the pathway of localizedtissue heating. Thus, the tissue is parted along the pathway ofevaporated cellular fluid, inducing undesirable collateral tissue damagein regions surrounding the target tissue site. This collateral tissuedamage often causes indiscriminate destruction of tissue, resulting inthe loss of the proper function of the tissue. In addition, the devicedoes not remove any tissue directly, but rather depends on destroying azone of tissue and allowing the body to eventually remove the destroyedtissue.

[0014] Many patients experience discogenic pain due to containedherniation of an intervertebral disc. Contained herniation often causespain due to nerve root compression resulting from protrusion of thenucleus pulposus into the annulus fibrosus and concomitant bulging ofthe annulus fibrosus at the disc perimeter. In many patients for whommajor spinal surgery is not indicated, discogenic pain resulting fromcontained herniation naturally diminishes in severity over an extendedperiod of time, perhaps several months. There is a need for minimallyinvasive methods to treat patients having contained herniation of anintervertebral disc, in order to alleviate the chronic, and oftendebilitating, pain associated with spinal nerve root compression. Theinstant invention provides methods for ablating tissue from a discexperiencing a contained herniation, wherein the procedure alleviatesdiscogenic pain resulting from this disorder.

SUMMARY OF THE INVENTION

[0015] The present invention provides systems, apparatus, and methodsfor selectively applying electrical energy to structures within apatient's body, such as the intervertebral disc. The systems and methodsof the present invention are useful for shrinkage, ablation, resection,aspiration, and/or hemostasis of tissue and other body structures inopen and endoscopic spine surgery. In particular, the present inventionincludes a method and system for debulking, ablating, and shrinking adisc in the cervical, thoracic or lumbar regions of the spine

[0016] The present invention further relates to an electrosurgical probeincluding an elongated shaft having first and second curves in thedistal end portion of the shaft, wherein the shaft can be rotated withinan intervertebral disc to contact tissue of the nucleus pulposus. Thepresent invention also relates to an electrosurgical probe including anelongated shaft, wherein the shaft distal end can be guided to aspecific target site within a disc, and the shaft distal end is adaptedfor localized ablation of targeted disc tissue. The present inventionfurther relates to a probe having an elongated shaft, wherein the shaftincludes an active electrode, an insulating collar, and an outer shield,and wherein the active electrode includes a head having an apical spikeand a cusp. The present invention still further relates to a method forablating disc tissue with an electrosurgical probe, wherein the probeincludes an elongated shaft, and the shaft distal end is guided to aspecific target site within a disc.

[0017] In one aspect, the present invention provides a method oftreating a herniated intervertebral disc. The method comprisespositioning at least one active electrode within the intervertebraldisc. High frequency voltage is applied between the active electrode(s)and one or more return electrode(s) to debulk, ablate, coagulate, and/orshrink at least a portion of the nucleus pulposus and/or annulus. In oneembodiment, the high frequency voltage is selected to ablate tissuewithin the nucleus. In other embodiments, the high frequency voltage isselected to effect a controlled depth of thermal heating to reduce thewater content of the nucleus pulposus, thereby debulking the nucleuspulposus and reducing the internal pressure on the annulus fibrosus.

[0018] In an exemplary embodiment, an electrically conductive media,such as isotonic saline or an electrically conductive gel, is deliveredto the target site within the intervertebral disc prior to delivery ofthe high frequency energy. The conductive media will typically fill theentire target region such that the active electrode(s) are submergedthroughout the procedure. In other embodiments, the extracellularconductive fluid (e.g., the nucleus pulposus) in the patient's disc maybe used as a substitute for, or as a supplement to, the electricallyconductive media that is applied or delivered to the target site. Forexample, in some embodiments, an initial amount of conductive media isprovided to initiate the requisite conditions for ablation. Afterinitiation, the conductive fluid already present in the patient's tissueis used to sustain these conditions.

[0019] In another aspect, the present invention provides a method oftreating a disc having a contained herniation or fissure. The methodcomprises introducing an electrosurgical instrument into the patient'sintervertebral disc either percutaneously or through an open procedure.The instrument is steered or otherwise guided into close proximity tothe contained herniation or fissure and a high frequency voltage isapplied between an active electrode and a return electrode so as todebulk the nucleus pulposus adjacent the contained herniation orfissure. In some embodiments a conductive fluid is delivered into theintervertebral disc prior to applying the high frequency voltage toensure that sufficient conductive fluid exists for plasma formation andto conduct electric current between the active and return electrodes.Alternatively, the conductive fluid can be delivered to the target siteduring the procedure. The heating delivered through the electricallyconductive fluid debulks the nucleus pulposus, and reduces the pressureon the annulus fibrosus so as to reduce the pressure on the affectednerve root and alleviate neck and back pain.

[0020] In another aspect, the present invention provides a method fortreating degenerative intervertebral discs. The active electrode(s) areadvanced into the target disc tissue in an ablation mode, where the highfrequency voltage is sufficient to ablate or remove the nucleus pulposusthrough molecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel, saline and/or intracellular fluid) between the activeelectrode(s) and the tissue. Within the vaporized fluid, an ionizedplasma is formed and charged particles (e.g., electrons) cause themolecular breakdown or disintegration of several cell layers of thenucleus pulposus. This molecular dissociation is accompanied by thevolumetric removal of the tissue. This process can be preciselycontrolled to effect the volumetric removal of tissue as thin as 10microns to 150 microns with minimal heating of, or damage to,surrounding or underlying tissue structures. A more complete descriptionof this phenomena is described in commonly assigned U.S. Pat. No.5,697,882 the complete disclosure of which is incorporated herein byreference.

[0021] An apparatus according to the present invention generallyincludes a shaft having proximal and distal end portions, an activeelectrode at the distal end and one or more connectors for coupling theactive electrode to a source of high frequency electrical energy. Theprobe or catheter may assume a wide variety of configurations, with theprimary purpose being to introduce the electrode assembly into thepatient's disc (in an open or endoscopic procedure) and to permit thetreating physician to manipulate the electrode assembly from a proximalend of the shaft. The probe shafts can be flexible, curved, or steerableso as to allow the treating physician to move the active electrode intoclose proximity of the herniation. The electrode assembly includes oneor more active electrode(s) and a return electrode spaced from theactive electrode(s) either on the instrument shaft or separate from theinstrument shaft.

[0022] The active electrode(s) may comprise a single active electrode,or an electrode array, extending from an electrically insulating supportmember, typically made of an inorganic material such as a ceramic, asilicone or a glass. The active electrode will usually have a smallerexposed surface area than the return such that the current densities aremuch higher at the active electrode than at the return electrode.Preferably, the return electrode has a relatively large, smooth surfacesextending around the instrument shaft to reduce current densities,thereby minimizing damage to adjacent tissue.

[0023] In another aspect, the present invention provides a method ofusing an electrosurgical system for treating a contained herniation ofan intervertebral disc of a patient, wherein the electrosurgical systemincludes a power supply coupled to at least one active electrodedisposed on a shaft distal end of an electrosurgical probe. Typically,the contained herniation includes a protrusion or bulge of the nucleuspulposus, wherein the bulge of the nucleus pulposus is contained within(i.e. does not breach) the annulus fibrosus of the disc. The methodincludes inserting the shaft distal end within the intervertebral discsuch that the at least one active electrode is in the vicinity of thecontained herniation, and thereafter applying a high frequency voltagebetween the at least one active electrode and at least one returnelectrode, such that tissue in the vicinity of the contained herniationis ablated.

[0024] The shaft may be guided by a combination of axial translation ofthe shaft and rotation of the shaft about its longitudinal axis. In oneaspect of the invention, the shaft has a pre-defined curvature, bothbefore and after the shaft has been guided to the vicinity of thecontained herniation. The pre-defined curvature may include a first anda second curve in the shaft, the second curve being proximal to thefirst curve.

[0025] By applying a high frequency voltage between the at least oneactive electrode and at least one return electrode, disc tissue in thevicinity of the contained herniation undergoes molecular dissociation.In one embodiment, the at least one active electrode includes anelectrode head having an apical spike and a cusp, wherein the electrodehead is adapted for providing a high current density in the vicinity ofthe electrode head when the high frequency voltage is applied betweenthe at least one active electrode and the return electrode. The methodmay be conveniently performed percutaneously, and one or more stages inthe treatment or procedure may be performed under fluoroscopy to allowvisualization of the shaft within the disc to be treated.

[0026] For a further understanding of the nature and advantages of theinvention, reference should be made to the following description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a perspective view of an electrosurgical systemincorporating a power supply and an electrosurgical probe for tissueablation, resection, incision, contraction and for vessel hemostasisaccording to the present invention;

[0028]FIG. 2 schematically illustrates one embodiment of a power supplyaccording to the present invention;

[0029]FIG. 3 illustrates an electrosurgical system incorporating aplurality of active electrodes and associated current limiting elements;

[0030]FIG. 4 is a side view of an electrosurgical probe according to thepresent invention;

[0031]FIG. 5 is a view of the distal end portion of the probe of FIG. 2

[0032]FIG. 6 is an exploded view of a proximal portion of theelectrosurgical probe;

[0033]FIGS. 7A and 7B are perspective and end views, respectively, of analternative electrosurgical probe incorporating an inner fluid lumen;

[0034] FIGS. 8A-8C are cross-sectional views of the distal portions ofthree different embodiments of an electrosurgical probe according to thepresent invention;

[0035] FIGS. 9-12 are end views of alternative embodiments of the probeof FIG. 4, incorporating aspiration electrode(s);

[0036]FIG. 13 is a side view of the distal portion of the shaft of anelectrosurgical probe, according to one embodiment of the invention;

[0037] FIGS. 14A-14C illustrate an alternative embodiment incorporatinga screen electrode;

[0038] FIGS. 15A-15D illustrate four embodiments of electrosurgicalprobes specifically designed for treating spinal defects;

[0039]FIG. 16 illustrates an electrosurgical system incorporating adispersive return pad for monopolar and/or bipolar operations;

[0040]FIG. 17 illustrates a catheter system for electrosurgicaltreatment of intervertebral discs according to the present invention;

[0041] FIGS. 18-22 illustrate a method of performing a microendoscopicdiscectomy according to the principles of the present invention;

[0042] FIGS. 23-25 illustrates another method of treating a spinal discwith one of the catheters or probes of the present invention;

[0043]FIG. 26A is a side view of an electrosurgical probe according tothe invention;

[0044]FIG. 26B is a side view of the distal end portion of theelectrosurgical probe of FIG. 26A;

[0045]FIG. 27A is a side view of an electrosurgical probe having acurved shaft;

[0046]FIG. 27B is a side view of the distal end portion of the curvedshaft of FIG. 27A, with the shaft distal end portion within anintroducer device;

[0047]FIG. 27C is a side view of the distal end portion of the curvedshaft of FIG. 27B in the absence of the introducer device;

[0048]FIG. 28A is a side view of the distal end portion of anelectrosurgical probe showing an active electrode having an apical spikeand an equatorial cusp;

[0049]FIG. 28B is a cross-sectional view of the distal end portion ofthe electrosurgical probe of FIG. 28A;

[0050]FIG. 29 is a side view of the distal end portion a shaft of anelectrosurgical probe, indicating the position of a first curve and asecond curve in relation to the head of the active electrode;

[0051]FIG. 30A shows the distal end portion of the shaft of anelectrosurgical probe extended distally from an introducer needle;

[0052]FIG. 30B illustrates the position of the active electrode inrelation to the inner wall of the introducer needle upon retraction ofthe active electrode within the introducer needle;

[0053]FIGS. 31A, 31B show a side view and an end view, respectively, ofa curved shaft of an electrosurgical probe, in relation to an introducerneedle;

[0054]FIG. 32A shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a plurality of depthmarkings;

[0055]FIG. 32B shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a mechanical stop;

[0056]FIG. 33 illustrates stages in manufacture of an active electrodeof an electrosurgical probe of the present invention;

[0057]FIG. 34 schematically represents a series of steps involved in amethod of making a probe shaft of the present invention;

[0058]FIG. 35 schematically represents a series of steps involved in amethod of making an electrosurgical probe of the present invention;

[0059]FIG. 36A schematically represents a normal intervertebral disc inrelation to the spinal cord;

[0060]FIG. 36B schematically represents an intervertebral discexhibiting a protrusion of the nucleus pulposus and a concomitantdistortion of the annulus fibrosus;

[0061]FIG. 36C schematically represents an intervertebral discexhibiting a plurality of fissures within the annulus fibrosus and aconcomitant distortion of the annulus fibrosus;

[0062]FIG. 36D schematically represents an intervertebral discexhibiting fragmentation of the nucleus pulposus and a concomitantdistortion of the annulus fibrosus;

[0063]FIG. 37 schematically represents translation of a curved shaft ofan electrosurgical probe within the nucleus pulposus for treatment of anintervertebral disc;

[0064]FIG. 38 shows a shaft of an electrosurgical probe within anintervertebral disc, wherein the shaft distal end is targeted to aspecific site within the disc;

[0065]FIG. 39 schematically represents a series of steps involved in amethod of ablating disc tissue according to the present invention;

[0066]FIG. 40 schematically represents a series of steps involved in amethod of guiding an electrosurgical probe to a target site within anintervertebral disc for ablation of targeted disc tissue, according toanother embodiment of the invention;

[0067]FIG. 41 shows treatment of an intervertebral disc using anelectrosurgical probe and a separately introduced ancillary device,according to another embodiment of the invention;

[0068]FIG. 42 is a side view of an electrosurgical probe having atracking device;.

[0069]FIG. 43A shows a steerable electrosurgical probe wherein the shaftof the probe assumes a substantially linear configuration;

[0070]FIG. 43B shows the steerable electrosurgical probe of FIG. 44A,wherein the shaft distal end of the probe adopts a bent configuration;and

[0071]FIG. 44 shows a steerable electrosurgical probe and an ancillarydevice inserted within the nucleus pulposus of an intervertebral disc.

DESCRIPTION OF SPECIFIC EMBODIMENTS

[0072] The present invention provides systems and methods forselectively applying electrical energy to a target location within or ona patient's body, particularly including support tissue or other bodystructures in the spine. These procedures include treating interspinoustissue, degenerative discs, laminectomy/discectomy procedures fortreating herniated discs, decompressive laminectomy for stenosis in thelumbosacral and cervical spine, localized tears or fissures in theannulus, nucleotomy, disc fusion procedures, medial facetectomy,posterior lumbosacral and cervical spine fusions, treatment of scoliosisassociated with vertebral disease, foraminotomies to remove the roof ofthe intervertebral foramina to relieve nerve root compression andanterior cervical and lumbar discectomies. These procedures may beperformed through open procedures, or using minimally invasivetechniques, such as thoracoscopy, arthroscopy, laparascopy or the like.

[0073] The present invention involves techniques for treating discabnormalities with RF energy. In some embodiments, RF energy is used toablate, debulk and/or stiffen the tissue structure of the disc to reducethe volume of the disc, thereby relieving neck and back pain. In oneaspect of the invention, spinal disc tissue is volumetrically removed orablated to form holes, channels, divots or other spaces within the disc.In this procedure, a high frequency voltage difference is appliedbetween one or more active electrode(s) and one or more returnelectrode(s) to develop high electric field intensities in the vicinityof the target tissue. The high electric field intensities adjacent theactive electrode(s) lead to electric field induced molecular breakdownof target tissue through molecular dissociation (rather than thermalevaporation or carbonization). Applicant believes that the tissuestructure is volumetrically removed through molecular disintegration oflarger organic molecules into smaller molecules and/or atoms, such ashydrogen, oxygen, oxides of carbon, hydrocarbons and nitrogen compounds.This molecular disintegration completely removes the tissue structure,as opposed to dehydrating the tissue material by the removal of liquidwithin the cells of the tissue and extracellular fluids, as is typicallythe case with electrosurgical desiccation and vaporization.

[0074] The present invention also involves a system and method fortreating the interspinous tissue (e.g., tendons, cartilage, synovialtissue in between the vertebrae, and other support tissue within andsurrounding the vertebral column). In some embodiments, RF energy isused to heat and shrink the interspinous tissue to stabilize thevertebral column and reduce pain in the back and neck. In one aspect ofthe invention, an active electrode is positioned adjacent theinterspinous tissue and the interspinous tissue is heated, preferablywith RF energy, to a sufficient temperature to shrink the interspinoustissue. In a specific embodiment, a high frequency voltage difference isapplied between one or more active electrode(s) and one or more returnelectrode(s) to develop high electric field intensities in the vicinityof the target tissue to controllably heat the target tissue.

[0075] The high electric field intensities may be generated by applyinga high frequency voltage that is sufficient to vaporize an electricallyconductive fluid over at least a portion of the active electrode(s) inthe region between the distal tip of the active electrode(s) and thetarget tissue. The electrically conductive fluid may be a liquid or gas,such as isotonic saline, blood, extracelluar or intracellular fluid,delivered to, or already present at, the target site, or a viscousfluid, such as a gel, applied to the target site. Since the vapor layeror vaporized region has a relatively high electrical impedance, itminimizes the current flow into the electrically conductive fluid. Thisionization, under the conditions described herein, induces the dischargeof energetic electrons and photons from the vapor layer and to thesurface of the target tissue A more detailed description of thisphenomena, termed Coblation® can be found in commonly assigned U.S. Pat.No. 5,697,882 the complete disclosure of which is incorporated herein byreference.

[0076] Applicant believes that the principle mechanism of tissue removalin the Coblation® mechanism of the present invention is energeticelectrons or ions that have been energized in a plasma adjacent to theactive electrode(s). When a liquid is heated enough that atoms vaporizeoff the surface faster than they recondense, a gas is formed. When thegas is heated enough that the atoms collide with each other and knocktheir electrons off in the process, an ionized gas or plasma is formed(the so-called “fourth state of matter”). A more complete description ofplasma can be found in Plasma Physics, by R. J. Goldston and P. H.Rutherford of the Plasma Physics Laboratory of Princeton University(1995), the complete disclosure of which is incorporated herein byreference. When the density of the vapor layer (or within a bubbleformed in the electrically conducting liquid) becomes sufficiently low(i.e., less than approximately 10²⁰ atoms/cm³ for aqueous solutions),the electron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Once the ionic particles in the plasmalayer have sufficient energy, they accelerate towards the target tissue.Energy evolved by the energetic electrons (e.g., 3.5 eV to 5 eV) cansubsequently bombard a molecule and break its bonds, dissociating amolecule into free radicals, which then combine into final gaseous orliquid species.

[0077] Plasmas may be formed by heating a gas and ionizing the gas bydriving an electric current through it, or by shining radio waves intothe gas. Generally, these methods of plasma formation give energy tofree electrons in the plasma directly, and then electron-atom collisionsliberate more electrons, and the process cascades until the desireddegree of ionization is achieved. Often, the electrons carry theelectrical current or absorb the radio waves and, therefore, are hotterthan the ions. Thus, in applicant's invention, the electrons, which arecarried away from the tissue towards the return electrode, carry most ofthe plasma's heat with them, allowing the ions to break apart the tissuemolecules in a substantially non-thermal manner.

[0078] In some embodiments, the present invention applies high frequency(RF) electrical energy in an electrically conducting media environmentto shrink or remove (i.e., resect, cut, or ablate) a tissue structureand to seal transected vessels within the region of the target tissue.The present invention may also be useful for sealing larger arterialvessels, e.g., on the order of about 1 mm in diameter. In someembodiments, a high frequency power supply is provided having anablation mode, wherein a first voltage is applied to an active electrodesufficient to effect molecular dissociation or disintegration of thetissue, and a coagulation mode, wherein a second, lower voltage isapplied to an active electrode (either the same or a differentelectrode) sufficient to heat, shrink, and/or achieve hemostasis ofsevered vessels within the tissue. In other embodiments, anelectrosurgical instrument is provided having one or more coagulationelectrode(s) configured for sealing a severed vessel, such as anarterial vessel, and one or more active electrodes configured for eithercontracting the collagen fibers within the tissue or removing (ablating)the tissue, e.g., by applying sufficient energy to the tissue to effectmolecular dissociation. In the latter embodiments, the coagulationelectrode(s) may be configured such that a single voltage can be appliedto coagulate with the coagulation electrode(s), and to ablate or shrinkwith the active electrode(s). In other embodiments, the power supply iscombined with the coagulation instrument such that the coagulationelectrode is used when the power supply is in the coagulation mode (lowvoltage), and the active electrode(s) are used when the power supply isin the ablation mode (higher voltage).

[0079] In one method of the present invention, one or more activeelectrodes are brought into close proximity to tissue at a target site,and the power supply is activated in the ablation mode such thatsufficient voltage is applied between the active electrodes and thereturn electrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the active electrodes may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent instrument may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

[0080] In another aspect, the present invention may be used to shrink orcontract collagen connective tissue which support the vertebral columnor connective tissue within the disc. In these procedures, the RF energyheats the tissue directly by virtue of the electrical current flowtherethrough, and/or indirectly through the exposure of the tissue tofluid heated by RF energy, to elevate the tissue temperature from normalbody temperatures (e.g., 37° C.) to temperatures in the range of 45° C.to 90° C., preferably in the range from about 60° C. to 70° C. Thermalshrinkage of collagen fibers occurs within a small temperature rangewhich, for mammalian collagen is in the range from 60° C. to 70° C.(Deak, G., et al., “The Thermal Shrinkage Process of Collagen Fibres asRevealed by Polarization Optical Analysis of Topooptical StainingReactions,” Acta Morphological Acad. Sci. of Hungary, Vol. 15(2), pp.195-208, 1967). Collagen fibers typically undergo thermal shrinkage inthe range of 60° C. to about 70° C. Previously reported research hasattributed thermal shrinkage of collagen to the cleaving of the internalstabilizing cross-linkages within the collagen matrix (Deak, ibid). Ithas also been reported that when the collagen temperature is increasedabove 70° C., the collagen matrix begins to relax again and theshrinkage effect is reversed resulting in no net shrinkage (Allain, J.C., et al., “Isometric Tensions Developed During the HydrothermalSwelling of Rat Skin,” Connective Tissue Research, Vol. 7, pp 127-133,1980), the complete disclosure of which is incorporated by reference.Consequently, the controlled heating of tissue to a precise depth iscritical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580 filed on Oct. 2, 1997, (Attorney DocketNo. 16238-001300), the complete disclosure of which is incorporated byreference.

[0081] The preferred depth of heating to effect the shrinkage ofcollagen in the heated region (i.e., the depth to which the tissue iselevated to temperatures between 60° C. to 70° C.) generally depends on(1) the thickness of the target tissue, (2) the location of nearbystructures (e.g., nerves) that should not be exposed to damagingtemperatures, and/or (3) the location of the collagen tissue layerwithin which therapeutic shrinkage is to be effected. The depth ofheating is usually in the range from 1.0 mm to 5.0 mm. In someembodiments of the present invention, the tissue is purposely damaged ina thermal heating mode to create necrosed or scarred tissue at thetissue surface. The high frequency voltage in the thermal heating modeis below the threshold of ablation as described above, but sufficient tocause some thermal damage to the tissue immediately surrounding theelectrodes without vaporizing or otherwise debulking this tissue insitu. Typically, it is desired to achieve a tissue temperature in therange of about 60° C. to 100° C. to a depth of about 0.2 mm to 5 mm,usually about 1 mm to 2 mm. The voltage required for this thermal damagewill partly depend on the electrode configurations, the conductivity ofthe area immediately surrounding the electrodes, the time period inwhich the voltage is applied and the depth of tissue damage desired.With the electrode configurations described in this application (e.g.,FIGS. 15A-15D), the voltage level for thermal heating will usually be inthe range of about 20 volts rms to 300 volts rms, preferably about 60volts rms to 200 volts rms. The peak-to-peak voltages for thermalheating with a square wave form having a crest factor of about 2 aretypically in the range of about 40 volts peak-to-peak to 600 voltspeak-to-peak, preferably about 120 volts peak-to-peak to 400 voltspeak-to-peak. In some embodiments, capacitors or other electricalelements may be used to increase the crest factor up to 10. The higherthe voltage is within this range, the less time required. If the voltageis too high, however, the surface tissue may be vaporized, debulked orablated, which is generally undesirable.

[0082] In yet another embodiment, the present invention may be used fortreating degenerative discs with fissures or tears. In theseembodiments, the active and return electrode(s) are positioned in oraround the inner wall of the disc annulus such that the active electrodeis adjacent to the fissure. High frequency voltage is applied betweenthe active and return electrodes to heat the fissure and shrink thecollagen fibers and create a seal or weld within the inner wall, therebyhelping to close the fissure in the annulus. In these embodiments, thereturn electrode will typically be positioned proximally from the activeelectrode(s) on the instrument shaft, and an electrically conductivefluid will be applied to the target site to create the necessary currentpath between the active and return electrodes. In alternativeembodiments, the disc tissue may complete this electrically conductivepath.

[0083] The present invention is also useful for removing or ablatingtissue around nerves, such as spinal, peripheral or cranial nerves. Oneof the significant drawbacks with the prior art shavers ormicrodebriders, conventional electrosurgical devices and lasers is thatthese devices do not differentiate between the target tissue and thesurrounding nerves or bone. Therefore, the surgeon must be extremelycareful during these procedures to avoid damage to the bone or nerveswithin and around the target site. In the present invention, theCoblation® process for removing tissue results in extremely small depthsof collateral tissue damage as discussed above. This allows the surgeonto remove tissue close to a nerve without causing collateral damage tothe nerve fibers.

[0084] In addition to the generally precise nature of the novelmechanisms of the present invention, applicant has discovered anadditional method of ensuring that adjacent nerves are not damagedduring tissue removal. According to the present invention, systems andmethods are provided for distinguishing between the fatty tissueimmediately surrounding nerve fibers and the normal tissue that is to beremoved during the procedure. Peripheral nerves usually comprise aconnective tissue sheath, or epineurium, enclosing the bundles of nervefibers, each bundle being surrounded by its own sheath of connectivetissue (the perineurium) to protect these nerve fibers. The outerprotective tissue sheath or epineurium typically comprises a fattytissue (e.g., adipose tissue) having substantially different electricalproperties than the normal target tissue, such as the turbinates,polyps, mucus tissue or the like, that are, for example, removed fromthe nose during sinus procedures. The system of the present inventionmeasures the electrical properties of the tissue at the tip of the probewith one or more active electrode(s). These electrical properties mayinclude electrical conductivity at one, several or a range offrequencies (e.g., in the range from 1 kHz to 100 MHz), dielectricconstant, capacitance or combinations of these. In this embodiment, anaudible signal may be produced when the sensing electrode(s) at the tipof the probe detects the fatty tissue surrounding a nerve, or directfeedback control can be provided to only supply power to the activeelectrode(s) either individually or to the complete array of electrodes,if and when the tissue encountered at the tip or working end of theprobe is normal tissue based on the measured electrical properties. Inone embodiment, the current limiting elements (discussed in detailabove) are configured such that the active electrodes will shut down orturn off when the electrical impedance reaches a threshold level. Whenthis threshold level is set to the impedance of the fatty tissuesurrounding nerves, the active electrodes will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother active electrodes, which are in contact with or in close proximityto tissue, will continue to conduct electric current to the returnelectrode. This selective ablation or removal of lower impedance tissuein combination with the Coblation® mechanism of the present inventionallows the surgeon to precisely remove tissue around nerves or bone.Applicant has found that the present invention is capable ofvolumetrically removing tissue closely adjacent to nerves withoutimpairment the function of the nerves, and without significantlydamaging the tissue of the epineurium. One of the significant drawbackswith the prior art microdebriders, conventional electrosurgical devicesand lasers is that these devices do not differentiate between the targettissue and the surrounding nerves or bone. Therefore, the surgeon mustbe extremely careful during these procedures to avoid damage to the boneor nerves within and around the nasal cavity. In the present invention,the Coblation® process for removing tissue results in extremely smalldepths of collateral tissue damage as discussed above. This allows thesurgeon to remove tissue close to a nerve without causing collateraldamage to the nerve fibers.

[0085] In addition to the above, applicant has discovered that theCoblation® mechanism of the present invention can be manipulated toablate or remove certain tissue structures, while having little effecton other tissue structures. As discussed above, the present inventionuses a technique of vaporizing electrically conductive fluid to form aplasma layer or pocket around the active electrode(s), and then inducingthe discharge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 10²⁰ atoms/cm³ for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 eV to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

[0086] The energy evolved by the energetic electrons may be varied byadjusting a variety of factors, such as: the number of activeelectrodes; electrode size and spacing; electrode surface area;asperities and sharp edges on the electrode surfaces; electrodematerials; applied voltage and power; current limiting means, such asinductors; electrical conductivity of the fluid in contact with theelectrodes; density of the fluid; and other factors. Accordingly, thesefactors can be manipulated to control the energy level of the excitedelectrons. Since different tissue structures have different molecularbonds, the present invention can be configured to break the molecularbonds of certain tissue, while having too low an energy to break themolecular bonds of other tissue. For example, fatty tissue, (e.g.,adipose) tissue has double bonds that require a substantially higherenergy level than 4 eV to 5 eV to break (typically on the order of about8 eV). Accordingly, the present invention in its current configurationgenerally does not ablate or remove such fatty tissue. However, thepresent invention may be used to effectively ablate cells to release theinner fat content in a liquid form. Of course, factors may be changedsuch that these double bonds can also be broken in a similar fashion asthe single bonds (e.g., increasing voltage or changing the electrodeconfiguration to increase the current density at the electrode tips). Amore complete description of this phenomena can be found in co-pendingU.S. patent application Ser. No. 09/032,375, filed Feb. 27, 1998(Attorney Docket No. CB-3), the complete disclosure of which isincorporated herein by reference.

[0087] In yet other embodiments, the present invention provides systems,apparatus and methods for selectively removing tumors, e.g., facialtumors, or other undesirable body structures while minimizing the spreadof viable cells from the tumor. Conventional techniques for removingsuch tumors generally result in the production of smoke in the surgicalsetting, termed an electrosurgical or laser plume, which can spreadintact, viable bacterial or viral particles from the tumor or lesion tothe surgical team or to other portions of the patient's body. Thispotential spread of viable cells or particles has resulted in increasedconcerns over the proliferation of certain debilitating and fataldiseases, such as hepatitis, herpes, HIV and papillomavirus. In thepresent invention, high frequency voltage is applied between the activeelectrode(s) and one or more return electrode(s) to volumetricallyremove at least a portion of the tissue cells in the tumor through thedissociation or disintegration of organic molecules into non-viableatoms and molecules. Specifically, the present invention converts thesolid tissue cells into non-condensable gases that are no longer intactor viable, and thus, not capable of spreading viable tumor particles toother portions of the patient's brain or to the surgical staff. The highfrequency voltage is preferably selected to effect controlled removal ofthese tissue cells while minimizing substantial tissue necrosis tosurrounding or underlying tissue. A more complete description of thisphenomena can be found in co-pending U.S. patent application Ser. No.09/109,219, filed Jun. 30, 1998 (Attorney Docket No. CB-1), the completedisclosure of which is incorporated herein by reference.

[0088] The electrosurgical probe or catheter of the present inventioncan comprise a shaft or a handpiece having a proximal end and a distalend which supports one or more active electrode(s). The shaft orhandpiece may assume a wide variety of configurations, with the primarypurpose being to mechanically support the active electrode and permitthe treating physician to manipulate the electrode from a proximal endof the shaft. The shaft may be rigid or flexible, with flexible shaftsoptionally being combined with a generally rigid external tube formechanical support. Flexible shafts may be combined with pull wires,shape memory actuators, and other known mechanisms for effectingselective deflection of the distal end of the shaft to facilitatepositioning of the electrode array. The shaft will usually include aplurality of wires or other conductive elements running axiallytherethrough to permit connection of the electrode array to a connectorat the proximal end of the shaft.

[0089] For endoscopic procedures within the spine, the shaft will have asuitable diameter and length to allow the surgeon to reach the targetsite (e.g., a disc or vertebra) by delivering the shaft through thethoracic cavity, the abdomen or the like. Thus, the shaft will usuallyhave a length in the range of about 5.0 cm to 30.0 cm, and a diameter inthe range of about 0.2 mm to about 20 mm. Alternatively, the shaft maybe delivered directly through the patient's back in a posteriorapproach, which would considerably reduce the required length of theshaft. In any of these embodiments, the shaft may also be introducedthrough rigid or flexible endoscopes. Alternatively, the shaft may be aflexible catheter that is introduced through a percutaneous penetrationin the patient. Specific shaft designs will be described in detail inconnection with the figures hereinafter.

[0090] In an alternative embodiment, the probe may comprise a long, thinneedle (e.g., on the order of about 1 mm in diameter or less) that canbe percutaneously introduced through the patient's back directly intothe spine. The needle will include one or more active electrode(s) forapplying electrical energy to tissues within the spine. The needle mayinclude one or more return electrode(s), or the return electrode may bepositioned on the patient's back, as a dispersive pad. In eitherembodiment, sufficient electrical energy is applied through the needleto the active electrode(s) to either shrink the collagen fibers withinthe spinal disc, to ablate tissue within the disc, or to shrink supportfibers surrounding the vertebrae.

[0091] The electrosurgical instrument may also be a catheter that isdelivered percutaneously and/or endoluminally into the patient byinsertion through a conventional or specialized guide catheter, or theinvention may include a catheter having an active electrode or electrodearray integral with its distal end. The catheter shaft may be rigid orflexible, with flexible shafts optionally being combined with agenerally rigid external tube for mechanical support. Flexible shaftsmay be combined with pull wires, shape memory actuators, and other knownmechanisms for effecting selective deflection of the distal end of theshaft to facilitate positioning of the electrode or electrode array. Thecatheter shaft will usually include a plurality of wires or otherconductive elements running axially therethrough to permit connection ofthe electrode or electrode array and the return electrode to a connectorat the proximal end of the catheter shaft. The catheter shaft mayinclude a guide wire for guiding the catheter to the target site, or thecatheter may comprise a steerable guide catheter. The catheter may alsoinclude a substantially rigid distal end portion to increase the torquecontrol of the distal end portion as the catheter is advanced furtherinto the patient's body. Specific shaft designs will be described indetail in connection with the figures hereinafter.

[0092] The active electrode(s) are preferably supported within or by aninorganic insulating support positioned near the distal end of theinstrument shaft. The return electrode may be located on the instrumentshaft, on another instrument or on the external surface of the patient(i.e., a dispersive pad). The close proximity of nerves and othersensitive tissue in and around the spinal cord, however, makes a bipolardesign more preferable because this minimizes the current flow throughnon-target tissue and surrounding nerves. Accordingly, the returnelectrode is preferably either integrated with the instrument body, oranother instrument located in close proximity thereto. The proximal endof the instrument(s) will include the appropriate electrical connectionsfor coupling the return electrode(s) and the active electrode(s) to ahigh frequency power supply, such as an electrosurgical generator.

[0093] In some embodiments, the active electrode(s) have an activeportion or surface with surface geometries shaped to promote theelectric field intensity and associated current density along theleading edges of the electrodes. Suitable surface geometries may beobtained by creating electrode shapes that include preferential sharpedges, or by creating asperities or other surface roughness on theactive surface(s) of the electrodes. Electrode shapes according to thepresent invention can include the use of formed wire (e.g., by drawinground wire through a shaping die) to form electrodes with a variety ofcross-sectional shapes, such as square, rectangular, L or V shaped, orthe like. Electrode edges may also be created by removing a portion ofthe elongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

[0094] Additionally or alternatively, the active electrode surface(s)may be modified through chemical, electrochemical or abrasive methods tocreate a multiplicity of surface asperities on the electrode surface.These surface asperities will promote high electric field intensitiesbetween the active electrode surface(s) and the target tissue tofacilitate ablation or cutting of the tissue. For example, surfaceasperities may be created by etching the active electrodes with etchantshaving a pH less than 7.0 or by using a high velocity stream of abrasiveparticles (e.g., grit blasting) to create asperities on the surface ofan elongated electrode. A more detailed description of such electrodeconfigurations can be found in U.S. Pat. No. 5,843,019, the completedisclosure of which is incorporated herein by reference.

[0095] The return electrode is typically spaced proximally from theactive electrode(s) a suitable distance to avoid electrical shortingbetween the active and return electrodes in the presence of electricallyconductive fluid. In most of the embodiments described herein, thedistal edge of the exposed surface of the return electrode is spacedabout 0.5 mm to 25 mm from the proximal edge of the exposed surface ofthe active electrode(s), preferably about 1.0 mm to 5.0 mm. Of course,this distance may vary with different voltage ranges, conductive fluids,and depending on the proximity of tissue structures to active and returnelectrodes. The return electrode will typically have an exposed lengthin the range of about 1 mm to 20 mm.

[0096] The current flow path between the active electrodes and thereturn electrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductivefluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, hypotonic saline or a gas, such as argon). Theconductive gel may also be delivered to the target site to achieve aslower more controlled delivery rate of conductive fluid. In addition,the viscous nature of the gel may allow the surgeon to more easilycontain the gel around the target site (e.g., rather than attempting tocontain isotonic saline). A more complete description of an exemplarymethod of directing electrically conductive fluid between the active andreturn electrodes is described in U.S. Pat. No. 5,697,281, previouslyincorporated herein by reference. Alternatively, the body's naturalconductive fluids, such as blood or extracellular saline, may besufficient to establish a conductive path between the returnelectrode(s) and the active electrode(s), and to provide the conditionsfor establishing a vapor layer, as described above. However, conductivefluid that is introduced into the patient is generally preferred overblood because blood will tend to coagulate at certain temperatures. Inaddition, the patient's blood may not have sufficient electricalconductivity to adequately form a plasma in some applications.Advantageously, a liquid electrically conductive fluid (e.g., isotonicsaline) may be used to concurrently “bathe” the target tissue surface toprovide an additional means for removing any tissue, and to cool theregion of the target tissue ablated in the previous moment.

[0097] The power supply, or generator, may include a fluid interlock forinterrupting power to the active electrode(s) when there is insufficientconductive fluid around the active electrode(s). This ensures that theinstrument will not be activated when conductive fluid is not present,minimizing the tissue damage that may otherwise occur. A more completedescription of such a fluid interlock can be found in commonly assigned,co-pending U.S. application Ser. No. 09/058,336, filed Apr. 10, 1998(attorney Docket No. CB-4), the complete disclosure of which isincorporated herein by reference.

[0098] In some procedures, it may also be necessary to retrieve oraspirate the electrically conductive fluid and/or the non-condensablegaseous products of ablation. In addition, it may be desirable toaspirate small pieces of tissue or other body structures that are notcompletely disintegrated by the high frequency energy, or other fluidsat the target site, such as blood, mucus, the gaseous products ofablation, etc. Accordingly, the system of the present invention mayinclude one or more suction lumen(s) in the instrument, or on anotherinstrument, coupled to a suitable vacuum source for aspirating fluidsfrom the target site. In addition, the invention may include one or moreaspiration electrode(s) coupled to the distal end of the suction lumenfor ablating, or at least reducing the volume of, non-ablated tissuefragments that are aspirated into the lumen. The aspiration electrode(s)function mainly to inhibit clogging of the lumen that may otherwiseoccur as larger tissue fragments are drawn therein. The aspirationelectrode(s) may be different from the ablation active electrode(s), orthe same electrode(s) may serve both functions. A more completedescription of instruments incorporating aspiration electrode(s) can befound in commonly assigned, co-pending U.S. patent application Ser. No.09/010,382 filed Jan. 21, 1998, the complete disclosure of which isincorporated herein by reference.

[0099] As an alternative or in addition to suction, it may be desirableto contain the excess electrically conductive fluid, tissue fragmentsand/or gaseous products of ablation at or near the target site with acontainment apparatus, such as a basket, retractable sheath, or thelike. This embodiment has the advantage of ensuring that the conductivefluid, tissue fragments or ablation products do not flow through thepatient's vasculature or into other portions of the body. In addition,it may be desirable to limit the amount of suction to limit theundesirable effect suction may have on hemostasis of severed bloodvessels.

[0100] The present invention may use a single active electrode or anarray of active electrodes spaced around the distal surface of acatheter or probe. In the latter embodiment, the electrode array usuallyincludes a plurality of independently current-limited and/orpower-controlled active electrodes to apply electrical energyselectively to the target tissue while limiting the unwanted applicationof electrical energy to the surrounding tissue and environment resultingfrom power dissipation into surrounding electrically conductive fluids,such as blood, normal saline, and the like. The active electrodes may beindependently current-limited by isolating the terminals from each otherand connecting each terminal to a separate power source that is isolatedfrom the other active electrodes. Alternatively, the active electrodesmay be connected to each other at either the proximal or distal ends ofthe catheter to form a single wire that couples to a power source.

[0101] In one configuration, each individual active electrode in theelectrode array is electrically insulated from all other activeelectrodes in the array within said instrument and is connected to apower source which is isolated from each of the other active electrodesin the array or to circuitry which limits or interrupts current flow tothe active electrode when low resistivity material (e.g., blood,electrically conductive saline irrigant or electrically conductive gel)causes a lower impedance path between the return electrode and theindividual active electrode. The isolated power sources for eachindividual active electrode may be separate power supply circuits havinginternal impedance characteristics which limit power to the associatedactive electrode when a low impedance return path is encountered. By wayof example, the isolated power source may be a user selectable constantcurrent source. In this embodiment, lower impedance paths willautomatically result in lower resistive heating levels since the heatingis proportional to the square of the operating current times theimpedance. Alternatively, a single power source may be connected to eachof the active electrodes through independently actuatable switches, orby independent current limiting elements, such as inductors, capacitors,resistors and/or combinations thereof. The current limiting elements maybe provided in the instrument, connectors, cable, controller, or alongthe conductive path from the controller to the distal tip of theinstrument. Alternatively, the resistance and/or capacitance may occuron the surface of the active electrode(s) due to oxide layers which formselected active electrodes (e.g., titanium or a resistive coating on thesurface of metal, such as platinum).

[0102] The tip region of the instrument may comprise many independentactive electrodes designed to deliver electrical energy in the vicinityof the tip. The selective application of electrical energy to theconductive fluid is achieved by connecting each individual activeelectrode and the return electrode to a power source havingindependently controlled or current limited channels. The returnelectrode(s) may comprise a single tubular member of conductive materialproximal to the electrode array at the tip which also serves as aconduit for the supply of the electrically conductive fluid between theactive and return electrodes. Alternatively, the instrument may comprisean array of return electrodes at the distal tip of the instrument(together with the active electrodes) to maintain the electric currentat the tip. The application of high frequency voltage between the returnelectrode(s) and the electrode array results in the generation of highelectric field intensities at the distal tips of the active electrodeswith conduction of high frequency current from each individual activeelectrode to the return electrode. The current flow from each individualactive electrode to the return electrode(s) is controlled by eitheractive or passive means, or a combination thereof, to deliver electricalenergy to the surrounding conductive fluid while minimizing energydelivery to surrounding (non-target) tissue.

[0103] The application of a high frequency voltage between the returnelectrode(s) and the active electrode(s) for appropriate time intervalseffects shrinking, cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. In some embodiments of thepresent invention, the tissue volume over which energy is dissipated(i.e., a high current density exists) may be more precisely controlled,for example, by the use of a multiplicity of small active electrodeswhose effective diameters or principal dimensions range from about 10 mmto 0.01 mm, preferably from about 2 mm to 0.05 mm, and more preferablyfrom about 1 mm to 0.1 mm. In this embodiment, electrode areas for bothcircular and non-circular terminals will have a contact area (per activeelectrode) below 50 mm² for electrode arrays and as large as 75 mm² forsingle electrode embodiments. In multiple electrode array embodiments,the contact area of each active electrode is typically in the range from0.0001 mm² to 1 mm², and more preferably from 0.001 mm² to 0.5 mm². Thecircumscribed area of the electrode array or active electrode is in therange from 0.25 mm² to 75 mm², preferably from 0.5 mm² to 40 mm². Inmultiple electrode embodiments, the array will usually include at leasttwo isolated active electrodes, often at least five active electrodes,often greater than 10 active electrodes and even 50 or more activeelectrodes, disposed over the distal contact surfaces on the shaft. Theuse of small diameter active electrodes increases the electric fieldintensity and reduces the extent or depth of tissue heating as aconsequence of the divergence of current flux lines which emanate fromthe exposed surface of each active electrode.

[0104] The area of the tissue treatment surface can vary widely, and thetissue treatment surface can assume a variety of geometries, withparticular areas and geometries being selected for specificapplications. The geometries can be planar, concave, convex,hemispherical, conical, linear “in-line” array or virtually any otherregular or irregular shape. Most commonly, the active electrode(s) oractive electrode(s) will be formed at the distal tip of theelectrosurgical instrument shaft, frequently being planar, disk-shaped,or hemispherical surfaces for use in reshaping procedures or beinglinear arrays for use in cutting. Alternatively or additionally, theactive electrode(s) may be formed on lateral surfaces of theelectrosurgical instrument shaft (e.g., in the manner of a spatula),facilitating access to certain body structures in endoscopic procedures.

[0105] It should be clearly understood that the invention is not limitedto electrically isolated active electrodes, or even to a plurality ofactive electrodes. For example, the array of active electrodes may beconnected to a single lead that extends through the catheter shaft to apower source of high frequency current. Alternatively, the instrumentmay incorporate a single electrode that extends directly through thecatheter shaft or is connected to a single lead that extends to thepower source. The active electrode(s) may have ball shapes (e.g., fortissue vaporization and desiccation), twizzle shapes (for vaporizationand needle-like cutting), spring shapes (for rapid tissue debulking anddesiccation), twisted metal shapes, annular or solid tube shapes or thelike. Alternatively, the electrode(s) may comprise a plurality offilaments, rigid or flexible brush electrode(s) (for debulking a tumor,such as a fibroid, bladder tumor or a prostate adenoma), side-effectbrush electrode(s) on a lateral surface of the shaft, coiledelectrode(s) or the like.

[0106] In some embodiments, the electrode support and the fluid outletmay be recessed from an outer surface of the instrument or handpiece toconfine the electrically conductive fluid to the region immediatelysurrounding the electrode support. In addition, the shaft may be shapedso as to form a cavity around the electrode support and the fluidoutlet. This helps to assure that the electrically conductive fluid willremain in contact with the active electrode(s) and the returnelectrode(s) to maintain the conductive path therebetween. In addition,this will help to maintain a vapor layer and subsequent plasma layerbetween the active electrode(s) and the tissue at the treatment sitethroughout the procedure, which reduces the thermal damage that mightotherwise occur if the vapor layer were extinguished due to a lack ofconductive fluid. Provision of the electrically conductive fluid aroundthe target site also helps to maintain the tissue temperature at desiredlevels.

[0107] In other embodiments, the active electrodes are spaced from thetissue a sufficient distance to minimize or avoid contact between thetissue and the vapor layer formed around the active electrodes. In theseembodiments, contact between the heated electrons in the vapor layer andthe tissue is minimized as these electrons travel from the vapor layerback through the conductive fluid to the return electrode. The ionswithin the plasma, however, will have sufficient energy, under certainconditions such as higher voltage levels, to accelerate beyond the vaporlayer to the tissue. Thus, the tissue bonds are dissociated or broken asin previous embodiments, while minimizing the electron flow, and thusthe thermal energy, in contact with the tissue.

[0108] The electrically conductive fluid should have a thresholdconductivity to provide a suitable conductive path between the returnelectrode and the active electrode(s). The electrical conductivity ofthe fluid (in units of millisiemens per centimeter or mS/cm) willusually be greater than 0.2 mS/cm, preferably will be greater than 2mS/cm and more preferably greater than 10 mS/cm. In an exemplaryembodiment, the electrically conductive fluid is isotonic saline, whichhas a conductivity of about 17 mS/cm. Applicant has found that a moreconductive fluid, or one with a higher ionic concentration, will usuallyprovide a more aggressive ablation rate. For example, a saline solutionwith higher levels of sodium chloride than conventional saline (which ison the order of about 0.9% sodium chloride) e.g., on the order ofgreater than 1% or between about 3% and 20%, may be desirable.Alternatively, the invention may be used with different types ofconductive fluids that increase the power of the plasma layer by, forexample, increasing the quantity of ions in the plasma, or by providingions that have higher energy levels than sodium ions. For example, thepresent invention may be used with elements other than sodium, such aspotassium, magnesium, calcium and other metals near the left end of theperiodic chart. In addition, other electronegative elements may be usedin place of chlorine, such as fluorine.

[0109] The voltage difference applied between the return electrode(s)and the active electrode(s) will be at high or radio frequency,typically between about 5 kHz and 20 MHz, usually being between about 30kHz and 2.5 MHz, preferably being between about 50 kHz and 500 kHz,often less than 350 kHz, and often between about 100 kHz and 200 kHz. Insome applications, applicant has found that a frequency of about 100 kHzis useful because the tissue impedance is much greater at thisfrequency. In other applications, such as procedures in or around theheart or head and neck, higher frequencies may be desirable (e.g.,400-600 kHz) to minimize low frequency current flow into the heart orthe nerves of the head and neck. The RMS (root mean square) voltageapplied will usually be in the range from about 5 volts to 1000 volts,preferably being in the range from about 10 volts to 500 volts, oftenbetween about 150 volts to 400 volts depending on the active electrodesize, the operating frequency and the operation mode of the particularprocedure or desired effect on the tissue (i.e., contraction,coagulation, cutting or ablation). Typically, the peak-to-peak voltagefor ablation or cutting with a square wave form will be in the range of10 volts to 2000 volts and preferably in the range of 100 volts to 1800volts and more preferably in the range of about 300 volts to 1500 volts,often in the range of about 300 volts to 800 volts peak to peak (again,depending on the electrode size, number of electrons, the operatingfrequency and the operation mode). Lower peak-to-peak voltages will beused for tissue coagulation, thermal heating of tissue, or collagencontraction and will typically be in the range from 50 to 1500,preferably 100 to 1000 and more preferably 120 to 400 volts peak-to-peak(again, these values are computed using a square wave form). Higherpeak-to-peak voltages, e.g., greater than about 800 volts peak-to-peak,may be desirable for ablation of harder material, such as bone,depending on other factors, such as the electrode geometries and thecomposition of the conductive fluid.

[0110] As discussed above, the voltage is usually delivered in a seriesof voltage pulses or alternating current of time varying voltageamplitude with a sufficiently high frequency (e.g., on the order of 5kHz to 20 MHz) such that the voltage is effectively applied continuously(as compared with e.g., lasers claiming small depths of necrosis, whichare generally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle(i.e., cumulative time in any one-second interval that energy isapplied) is on the order of about 50% for the present invention, ascompared with pulsed lasers which typically have a duty cycle of about0.0001%.

[0111] The preferred power source of the present invention delivers ahigh frequency current selectable to generate average power levelsranging from several milliwatts to tens of watts per electrode,depending on the volume of target tissue being treated, and/or themaximum allowed temperature selected for the instrument tip. The powersource allows the user to select the voltage level according to thespecific requirements of a particular neurosurgery procedure, cardiacsurgery, arthroscopic surgery, dermatological procedure, ophthalmicprocedures, open surgery or other endoscopic surgery procedure. Forcardiac procedures and potentially for neurosurgery, the power sourcemay have an additional filter, for filtering leakage voltages atfrequencies below 100 kHz, particularly voltages around 60 kHz.Alternatively, a power source having a higher operating frequency, e.g.,300 kHz to 600 kHz may be used in certain procedures in which stray lowfrequency currents may be problematic. A description of one suitablepower source can be found in co-pending patent application Ser. Nos.09/058,571 and 09/058,336, filed Apr. 10, 1998 (Attorney Docket Nos.CB-2 and CB-4), the complete disclosure of both applications areincorporated herein by reference for all purposes.

[0112] The power source may be current limited or otherwise controlledso that undesired heating of the target tissue or surrounding(non-target) tissue does not occur. In a presently preferred embodimentof the present invention, current limiting inductors are placed inseries with each independent active electrode, where the inductance ofthe inductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously in U.S. Pat.No. 5,697,909, the complete disclosure of which is incorporated hereinby reference. Additionally, current limiting resistors may be selected.Preferably, these resistors will have a large positive temperaturecoefficient of resistance so that, as the current level begins to risefor any individual active electrode in contact with a low resistancemedium (e.g., saline irrigant or blood), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from said active electrode into the low resistance medium(e.g., saline irrigant or blood).

[0113] Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site, and a fluid source 21 for supplyingelectrically conductive fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site. The endoscope maybe integral with probe 10, or it may be part of a separate instrument.The system 11 may also include a vacuum source (not shown) for couplingto a suction lumen or tube 211 (see FIG. 4) in the probe 10 foraspirating the target site.

[0114] As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of active electrodes 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the active electrodes 58 to power supply 28. The activeelectrodes 58 are electrically isolated from each other and each ofelectrodes 58 is connected to an active or passive control networkwithin power supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conductive fluid 50 tothe target site. Fluid supply tube 15 may be connected to a suitablepump (not shown), if desired.

[0115] Power supply 28 has an operator controllable voltage leveladjustment 30 to change the applied voltage level, which is observableat a voltage level display 32. Power supply 28 also includes first,second and third foot pedals 37, 38, 39 and a cable 36 which isremovably coupled to power supply 28. The foot pedals 37, 38, 39 allowthe surgeon to remotely adjust the energy level applied to activeelectrodes 58. In an exemplary embodiment, first foot pedal 37 is usedto place the power supply into the “ablation” mode and second foot pedal38 places power supply 28 into the “sub-ablation” mode (e.g., forcoagulation or contraction of tissue). The third foot pedal 39 allowsthe user to adjust the voltage level within the “ablation” mode. In theablation mode, a sufficient voltage is applied to the active electrodesto establish the requisite conditions for molecular dissociation of thetissue (i.e., vaporizing a portion of the electrically conductive fluid,ionizing charged particles within the vapor layer and accelerating thesecharged particles against the tissue). As discussed above, the requisitevoltage level for ablation will vary depending on the number, size,shape and spacing of the electrodes, the distance in which theelectrodes extend from the support member, etc. Once the surgeon placesthe power supply in the “ablation” mode, voltage level adjustment 30 orthird foot pedal 39 may be used to adjust the voltage level to adjustthe degree or aggressiveness of the ablation.

[0116] Of course, it will be recognized that the voltage and modality ofthe power supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

[0117] In the subablation mode, the power supply 28 applies a low enoughvoltage to the active electrodes to avoid vaporization of theelectrically conductive fluid and subsequent molecular dissociation ofthe tissue. The surgeon may automatically toggle the power supplybetween the ablation and sub-ablation modes by alternately stepping onfoot pedals 37, 38, respectively. In some embodiments, this allows thesurgeon to quickly move between coagulation/thermal heating and ablationin situ, without having to remove his/her concentration from thesurgical field or without having to request an assistant to switch thepower supply. By way of example, as the surgeon is sculpting soft tissuein the ablation mode, the probe typically will simultaneously sealand/or coagulation small severed vessels within the tissue. However,larger vessels, or vessels with high fluid pressures (e.g., arterialvessels) may not be sealed in the ablation mode. Accordingly, thesurgeon can simply step on foot pedal 38, automatically lowering thevoltage level below the threshold level for ablation, and applysufficient pressure onto the severed vessel for a sufficient period oftime to seal and/or coagulate the vessel. After this is completed, thesurgeon may quickly move back into the ablation mode by stepping on footpedal 37.

[0118] Referring now to FIGS. 2 and 3, a representative high frequencypower supply for use according to the principles of the presentinvention will now be described. The high frequency power supply of thepresent invention is configured to apply a high frequency voltage ofabout 10 volts RMS to 500 volts RMS between one or more activeelectrodes (and/or coagulation electrode) and one or more returnelectrodes. In the exemplary embodiment, the power supply applies about70 volts RMS to 350 volts RMS in the ablation mode and about 20 volts to90 volts in a subablation mode, preferably 45 volts to 70 volts in thesubablation mode (these values will, of course, vary depending on theprobe configuration attached to the power supply and the desired mode ofoperation).

[0119] The preferred power source of the present invention delivers ahigh frequency current selectable to generate average power levelsranging from several milliwatts to tens of watts per electrode,depending on the volume of target tissue being treated, and/or themaximum allowed temperature selected for the probe tip. The power supplyallows the user to select the voltage level according to the specificrequirements of a particular procedure, e.g., spinal surgery,arthroscopic surgery, dermatological procedure, ophthalmic procedures,open surgery, or other endoscopic surgery procedure.

[0120] As shown in FIG. 2, the power supply generally comprises a radiofrequency (RF) power oscillator 70 having output connections forcoupling via a power output signal 71 to the load impedance, which isrepresented by the electrode assembly when the electrosurgical probe isin use. In the representative embodiment, the RF oscillator operates atabout 100 kHz. The RF oscillator is not limited to this frequency andmay operate at frequencies of about 300 kHz to 600 kHz. In particular,for cardiac applications, the RF oscillator will preferably operate inthe range of about 400 kHz to about 600 kHz. The RF oscillator willgenerally supply a square wave signal with a crest factor of about 1 to2. Of course, this signal may be a sine wave signal or other suitablewave signal depending on the application and other factors, such as thevoltage applied, the number and geometry of the electrodes, etc. Thepower output signal 71 is designed to incur minimal voltage decrease(i.e., sag) under load. This improves the applied voltage to the activeelectrodes and the return electrode, which improves the rate ofvolumetric removal (ablation) of tissue.

[0121] Power is supplied to RF oscillator 70 by a switching power supply72 coupled between the power line and the RF oscillator rather than aconventional transformer. The switching power supply 72 allows powersupply 28 to achieve high peak power output without the large size andweight of a bulky transformer. The architecture of the switching powersupply also has been designed to reduce electromagnetic noise such thatU.S. and foreign EMI requirements are met. This architecture comprises azero voltage switching or crossing, which causes the transistors to turnON and OFF when the voltage is zero. Therefore, the electromagneticnoise produced by the transistors switching is vastly reduced. In anexemplary embodiment, the switching power supply 72 operates at about100 kHz.

[0122] A controller 74 coupled to the operator controls 73 (i.e., footpedals and voltage selector) and display 76, is connected to a controlinput of the switching power supply 72 for adjusting the generatoroutput power by supply voltage variation. The controller 74 may be amicroprocessor or an integrated circuit. The power supply may alsoinclude one or more current sensors 75 for detecting the output current.The power supply is preferably housed within a metal casing whichprovides a durable enclosure for the electrical components therein. Inaddition, the metal casing reduces the electromagnetic noise generatedwithin the power supply because the grounded metal casing functions as a“Faraday shield,” thereby shielding the environment from internalsources of electromagnetic noise.

[0123] The power supply generally comprises a main or mother boardcontaining generic electrical components required for many differentsurgical procedures (e.g., arthroscopy, urology, general surgery,dermatology, neurosurgery, etc.), and a daughter board containingapplication specific current-limiting circuitry (e.g., inductors,resistors, capacitors and the like). The daughter board is coupled tothe mother board by a detachable multi-pin connector to allow convenientconversion of the power supply to, e.g., applications requiring adifferent current limiting circuit design. For arthroscopy, for example,the daughter board preferably comprises a plurality of inductors ofabout 200 to 400 microhenries, usually about 300 microhenries, for eachof the channels supplying current to the active electrodes 102 (see FIG.4).

[0124] Alternatively, in one embodiment, current limiting inductors areplaced in series with each independent active electrode, where theinductance of the inductor is in the range of 10 uH to 50,000 uH,depending on the electrical properties of the target tissue, the desiredtissue heating rate and the operating frequency. Alternatively,capacitor-inductor (LC) circuit structures may be employed, as describedpreviously in co-pending PCT application No. PCT/US94/05168, thecomplete disclosure of which is incorporated herein by reference.Additionally, current limiting resistors may be selected. Preferably,these resistors will have a large positive temperature coefficient ofresistance so that, as the current level begins to rise for anyindividual active electrode in contact with a low resistance medium(e.g., saline irrigant or conductive gel), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from said active electrode into the low resistance medium(e.g., saline irrigant or conductive gel). Power output signal may alsobe coupled to a plurality of current limiting elements 96, which arepreferably located on the daughter board since the current limitingelements may vary depending on the application. A more completedescription of a representative power supply can be found in commonlyassigned U.S. patent application Ser. No. 09/058,571, previouslyincorporated herein by reference.

[0125] FIGS. 4-6 illustrate an exemplary electrosurgical probe 20constructed according to the principles of the present invention. Asshown in FIG. 4, probe 20 generally includes an elongated shaft 100which may be flexible or rigid, a handle 204 coupled to the proximal endof shaft 100 and an electrode support member 102 coupled to the distalend of shaft 100. Shaft 100 preferably comprises an electricallyconducting material, usually metal, which is selected from the groupcomprising tungsten, stainless steel alloys, platinum or its alloys,titanium or its alloys, molybdenum or its alloys, and nickel or itsalloys. In this embodiment, shaft 100 includes an electricallyinsulating jacket 108, which is typically formed as one or moreelectrically insulating sheaths or coatings, such aspolytetrafluoroethylene, polyimide, and the like. The provision of theelectrically insulating jacket over the shaft prevents direct electricalcontact between these metal elements and any adjacent body structure orthe surgeon. Such direct electrical contact between a body structure(e.g., tendon) and an exposed electrode could result in unwanted heatingand necrosis of the structure at the point of contact causing necrosis.Alternatively, the return electrode may comprise an annular band coupledto an insulating shaft and having a connector extending within the shaftto its proximal end.

[0126] Handle 204 typically comprises a plastic material that is easilymolded into a suitable shape for handling by the surgeon. Handle 204defines an inner cavity (not shown) that houses the electricalconnections 250 (FIG. 6), and provides a suitable interface forconnection to an electrical connecting cable distal portion 22 (seeFIG. 1) Electrode support member 102 extends from the distal end ofshaft 100 (usually about 1 mm to 20 mm), and provides support for aplurality of electrically isolated active electrodes 104 (see FIG. 5).As shown in FIG. 4, a fluid tube 233 extends through an opening inhandle 204, and includes a connector 235 for connection to a fluidsupply source, for supplying electrically conductive fluid to the targetsite. Depending on the configuration of the distal surface of shaft 100,fluid tube 233 may extend through a single lumen (not shown) in shaft100, or it may be coupled to a plurality of lumens (also not shown) thatextend through shaft 100 to a plurality of openings at its distal end.In the representative embodiment, tubing 239 is a tube that extendsalong the exterior of shaft 100 to a point just distal of returnelectrode 112 (see FIG. 5). In this embodiment, the fluid is directedthrough an opening 237 past return electrode 112 to the activeelectrodes 104. Probe 20 may also include a valve 17 (FIG. 1) orequivalent structure for controlling the flow rate of the electricallyconductive fluid to the target site.

[0127] As shown in FIG. 4, the distal portion of shaft 100 is preferablybent to improve access to the operative site of the tissue beingtreated. Electrode support member 102 has a substantially planar tissuetreatment surface 212 (FIG. 5) that is usually at an angle of about 10degrees to 90 degrees relative to the longitudinal axis of shaft 100,preferably about 30 degrees to 60 degrees and more preferably about 45degrees. In alternative embodiments, the distal portion of shaft 100comprises a flexible material which can be deflected relative to thelongitudinal axis of the shaft. Such deflection may be selectivelyinduced by mechanical tension of a pull wire, for example, or by a shapememory wire that expands or contracts by externally applied temperaturechanges. A more complete description of this embodiment can be found inU.S. Pat. No. 5,697,909, the complete disclosure of which has previouslybeen incorporated herein by reference. Alternatively, the shaft 100 ofthe present invention may be bent by the physician to the appropriateangle using a conventional bending tool or the like.

[0128] In the embodiment shown in FIGS. 4 to 6, probe 20 includes areturn electrode 112 for completing the current path between activeelectrodes 104 and a high frequency power supply 28 (see FIG. 1). Asshown, return electrode 112 preferably comprises an exposed portion ofshaft 100 shaped as an annular conductive band near the distal end ofshaft 100 slightly proximal to tissue treatment surface 212 of electrodesupport member 102, typically about 0.5 mm to 10 mm and more preferablyabout 1 mm to 10 mm. Return electrode 112 or shaft 100 is coupled to aconnector 258 that extends to the proximal end of probe 10/20, where itis suitably connected to power supply 28 (FIG. 1).

[0129] As shown in FIG. 4, return electrode 112 is not directlyconnected to active electrodes 104. To complete this current path sothat active electrodes 104 are electrically connected to returnelectrode 112, an electrically conductive fluid (e.g., isotonic saline)is caused to flow therebetween. In the representative embodiment, theelectrically conductive fluid is delivered through fluid tube 233 toopening 237, as described above. Alternatively, the conductive fluid maybe delivered by a fluid delivery element (not shown) that is separatefrom probe 20. In arthroscopic surgery, for example, the target area ofthe joint will be flooded with isotonic saline and the probe 90 will beintroduced into this flooded target area. Electrically conductive fluidcan be continually resupplied to maintain the conduction path betweenreturn electrode 112 and active electrodes 104. In other embodiments,the distal portion of probe 20 may be dipped into a source ofelectrically conductive fluid, such as a gel or isotonic saline, priorto positioning at the target site. Applicant has found that the surfacetension of the fluid and/or the viscous nature of a gel allows theconductive fluid to remain around the active and return electrodes forlong enough to complete its function according to the present invention,as described below. Alternatively, the conductive fluid, such as a gel,may be applied directly to the target site.

[0130] In alternative embodiments, the fluid path may be formed in probe90 by, for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (see FIGS. 8Aand 8B). This annular gap may be formed near the perimeter of the shaft100 such that the electrically conductive fluid tends to flow radiallyinward towards the target site, or it may be formed towards the centerof shaft 100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in U.S. Pat. No.5,697,281, the complete disclosure of which has previously beenincorporated herein by reference.

[0131] Referring to FIG. 5, the electrically isolated active electrodes104 are spaced apart over tissue treatment surface 212 of electrodesupport member 102. The tissue treatment surface and individual activeelectrodes 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range of1 mm to 20 mm. The individual active electrodes 104 preferably extendoutward from tissue treatment surface 212 by a distance of about 0.1 mmto 4 mm, usually about 0.2 mm to 2 mm. Applicant has found that thisconfiguration increases the high electric field intensities andassociated current densities around active electrodes 104 to facilitatethe ablation and shrinkage of tissue as described in detail above.

[0132] In the embodiment of FIGS. 4 to 6, the probe includes a single,larger opening 209 in the center of tissue treatment surface 212, and aplurality of active electrodes (e.g., about 3-15) around the perimeterof surface 212 (see FIG. 5). Alternatively, the probe may include asingle, annular, or partially annular, active electrode at the perimeterof the tissue treatment surface. The central opening 209 is coupled to asuction lumen (not shown) within shaft 100 and a suction tube 211 (FIG.4) for aspirating tissue, fluids and/or gases from the target site. Inthis embodiment, the electrically conductive fluid generally flowsradially inward past active electrodes 104 and then back through theopening 209. Aspirating the electrically conductive fluid during surgeryallows the surgeon to see the target site, and it prevents the fluidfrom flowing into the patient's body.

[0133] Of course, it will be recognized that the distal tip of anelectrosurgical probe of the invention, e.g. probe 10/20/90, may have avariety of different configurations. For example, the probe may includea plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (see FIG. 7B). In this embodiment, the activeelectrodes 104 extend distally from the center of tissue treatmentsurface 212 such that they are located radially inward from openings209. The openings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and suction tube 211for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the active electrodes 104.

[0134]FIG. 6 illustrates the electrical connections 250 within handle204 for coupling active electrodes 104 and return electrode 112 to thepower supply 28. As shown, a plurality of wires 252 extend through shaft100 to couple active electrodes 104 to a plurality of pins 254, whichare plugged into a connector block 256 for coupling to a connectingcable distal end 22 (FIG. 1). Similarly, return electrode 112 is coupledto connector block 256 via a wire 258 and a plug 260.

[0135] According to the present invention, the probe 20 further includesan identification element that is characteristic of the particularelectrode assembly so that the same power supply 28 can be used fordifferent electrosurgical operations. In one embodiment, for example,the probe (e.g., 20) includes a voltage reduction element or a voltagereduction circuit for reducing the voltage applied between the activeelectrodes 104 and the return electrode 112. The voltage reductionelement serves to reduce the voltage applied by the power supply so thatthe voltage between the active electrodes and the return electrode islow enough to avoid excessive power dissipation into the electricallyconducting medium and/or ablation of the soft tissue at the target site.In some embodiments, the voltage reduction element allows the powersupply 28 to apply two different voltages simultaneously to twodifferent electrodes (see FIG. 15D). In other embodiments, the voltagereduction element primarily allows the electrosurgical probe to becompatible with various electrosurgical generators supplied byArthroCare Corporation (Sunnyvale, Calif.) that are adapted to applyhigher voltages for ablation or vaporization of tissue. For thermalheating or coagulation of tissue, for example, the voltage reductionelement will serve to reduce a voltage of about 100 volts rms to 170volts rms (which is a setting of 1 or 2 on the ArthroCare Model 970 and980 (i.e., 2000) Generators) to about 45 volts rms to 60 volts rms,which is a suitable voltage for coagulation of tissue without ablation(e.g., molecular dissociation) of the tissue.

[0136] Of course, for some procedures, the probe will typically notrequire a voltage reduction element. Alternatively, the probe mayinclude a voltage increasing element or circuit, if desired.Alternatively or additionally, the cable 34 and/or cable distal end 22that couples the power supply 28 to the probe may be used as a voltagereduction element. The cable has an inherent capacitance that can beused to reduce the power supply voltage if the cable is placed into theelectrical circuit between the power supply, the active electrodes andthe return electrode. In this embodiment, the cable distal end 22 may beused alone, or in combination with one of the voltage reduction elementsdiscussed above, e.g., a capacitor. Further, it should be noted that thepresent invention can be used with a power supply that is adapted toapply a voltage within the selected range for treatment of tissue. Inthis embodiment, a voltage reduction element or circuitry may not bedesired.

[0137] FIGS. 8A-8C schematically illustrate the distal portion of threedifferent embodiments of probe 90 according to the present invention. Asshown in FIG. 8A, active electrodes 104 are anchored in a support matrix102′ of suitable insulating material (e.g., silicone or a ceramic orglass material, such as alumina, zirconia and the like) which could beformed at the time of manufacture in a flat, hemispherical or othershape according to the requirements of a particular procedure. Thepreferred support matrix material is alumina, available from KyoceraIndustrial Ceramics Corporation, Elkgrove, Ill., because of its highthermal conductivity, good electrically insulative properties, highflexural modulus, resistance to carbon tracking, biocompatibility, andhigh melting point. The support matrix 102′ is adhesively joined to atubular support member 78 that extends most or all of the distancebetween matrix 102′ and the proximal end of probe 90. Tubular member 78preferably comprises an electrically insulating material, such as anepoxy or silicone-based material.

[0138] In a preferred construction technique, active electrodes 104extend through pre-formed openings in the support matrix 102′ so thatthey protrude above tissue treatment surface 212 by the desireddistance. The electrodes are then bonded to the tissue treatment surface212 of support matrix 102′, typically by an inorganic sealing material80. Sealing material 80 is selected to provide effective electricalinsulation, and good adhesion to both support matrix 102′ and theplatinum or titanium active electrodes. Sealing material 80 additionallyshould have a compatible thermal expansion coefficient and a meltingpoint well below that of platinum or titanium and alumina or zirconia,typically being a glass or glass ceramic.

[0139] In the embodiment shown in FIG. 8A, return electrode 112comprises an annular member positioned around the exterior of shaft 100of probe 90. Return electrode 112 may fully or partially circumscribetubular support member 78 to form an annular gap 54 therebetween forflow of electrically conductive liquid 50 therethrough, as discussedbelow. Gap 54 preferably has a width in the range of 0.25 mm to 4 mm.Alternatively, probe 90 may include a plurality of longitudinal ribsbetween support member 78 and return electrode 112 to form a pluralityof fluid lumens extending along the perimeter of shaft 100. In thisembodiment, the plurality of lumens will extend to a plurality ofopenings.

[0140] Return electrode 112 is disposed within an electricallyinsulative jacket 118, which is typically formed as one or moreelectrically insulative sheaths or coatings, such aspolytetrafluoroethylene, polyimide, and the like. The provision of theelectrically insulative jacket 118 over return electrode 112 preventsdirect electrical contact between return electrode 112 and any adjacentbody structure. Such direct electrical contact between a body structure(e.g., tendon) and an exposed return electrode 112 could result inunwanted heating and necrosis of the structure at the point of contact.

[0141] As shown in FIG. 8A, return electrode 112 is not directlyconnected to active electrodes 104. To complete this current path sothat terminals 104 are electrically connected to return electrode 112,electrically conducting liquid 50 (e.g., isotonic saline) is caused toflow along fluid path(s) 83. Fluid path 83 is formed by annular gap 54between return electrode 112 and tubular support member 78. Theelectrically conducting liquid 50 flowing through fluid path 83 providesa pathway for electrical current flow between active electrodes 104 andreturn electrode 112, as illustrated by the current flux lines 60 inFIG. 8A. When a voltage difference is applied between active electrodes104 and return electrode 112, high electric field intensities will begenerated at the distal tips of active electrodes 104 with current flowfrom active electrodes 104 through the target tissue to return electrode112, the high electric field intensities causing ablation of tissue 52in zone 88.

[0142]FIG. 8B illustrates another alternative embodiment ofelectrosurgical probe 90 which has a return electrode 112 positionedwithin tubular member 78. Return electrode 112 is preferably a tubularmember defining an inner lumen 57 for allowing electrically conductingliquid 50 (e.g., isotonic saline) to flow therethrough in electricalcontact with return electrode 112. In this embodiment, a voltagedifference is applied between active electrodes 104 and return electrode112 resulting in electrical current flow through the electricallyconducting liquid 50 as shown by current flux lines 60. As a result ofthe applied voltage difference and concomitant high electric fieldintensities at the tips of active electrodes 104, tissue 52 becomesablated or transected in zone 88.

[0143]FIG. 8C illustrates another embodiment of probe 90 that is acombination of the embodiments in FIGS. 8A and 8B. As shown, this probeincludes both an inner lumen 57 and an outer gap or plurality of outerlumens 54 for flow of electrically conductive fluid. In this embodiment,the return electrode 112 may be positioned within tubular member 78 asin FIG. 8B, outside of tubular member 78 as in FIG. 8A, or in bothlocations.

[0144] In some embodiments, the probe 20/90 will also include one ormore aspiration electrode(s) coupled to the aspiration lumen forinhibiting clogging during aspiration of tissue fragments from thesurgical site. As shown in FIG. 9, one or more of the active electrodes104 may comprise loop electrodes 140 that extend across distal opening209 of the suction lumen within shaft 100. In the representativeembodiment, two of the active electrodes 104 comprise loop electrodes140 that cross over the distal opening 209. Of course, it will berecognized that a variety of different configurations are possible, suchas a single loop electrode, or multiple loop electrodes having differentconfigurations than shown. In addition, the electrodes may have shapesother than loops, such as the coiled configurations shown in FIGS. 10and 11. Alternatively, the electrodes may be formed within suction lumenproximal to the distal opening 209, as shown in FIG. 13. The mainfunction of loop electrodes 140 is to ablate portions of tissue that aredrawn into the suction lumen to prevent clogging of the lumen.

[0145] In some embodiments, loop electrodes 140 are electricallyisolated from the other active electrodes 104. In other embodiments, theloop electrodes 140 and active electrodes 104 may be electricallyconnected to each other such that both are activated together. Loopelectrodes 140 may or may not be electrically isolated from each other.Loop electrodes 140 will usually extend only about 0.05 mm to 4 mm,preferably about 0.1 mm to 1 mm from the tissue treatment surface ofelectrode support member 102.

[0146] Referring now to FIGS. 10 and 11, alternative embodiments foraspiration electrodes will now be described. As shown in FIG. 10, theaspiration electrodes may comprise a pair of coiled electrodes 150 thatextend across distal opening 209 of the suction lumen. The largersurface area of the coiled electrodes 150 usually increases theeffectiveness of the electrodes 150 in ablating tissue fragments whichmay approach or pass through opening 209. In FIG. 11, the aspirationelectrode comprises a single coiled electrode 154 extending across thedistal opening 209 of the suction lumen. This single electrode 152 maybe sufficient to inhibit clogging of the suction lumen. Alternatively,the aspiration electrodes may be positioned within the suction lumenproximal to the distal opening 209. Preferably, these electrodes areclose to opening 209 so that tissue does not clog the opening 209 beforeit reaches electrodes 154. In this embodiment, a separate returnelectrode (not shown) may be provided within the suction lumen toconfine the electric currents therein.

[0147] Referring to FIG. 12, another embodiment of the present inventionincorporates a wire mesh electrode 600 extending across the distalportion of aspiration lumen 162. As shown, mesh electrode 600 includes aplurality of openings 602 to allow fluids and tissue fragments to flowtherethrough into aspiration lumen 162. The size of the openings 602will vary depending on a variety of factors. The mesh electrode may becoupled to the distal or proximal surfaces of support member 102. Wiremesh electrode 600 comprises a conductive material, such as titanium,tantalum, steel, stainless steel, tungsten, copper, gold or the like. Inthe representative embodiment, wire mesh electrode 600 comprises adifferent material having a different electric potential than the activeelectrode(s) 104. Preferably, mesh electrode 600 comprises steel andactive electrode(s) 104 comprises tungsten. Applicant has found that aslight variance in the electrochemical potential of mesh electrode 600and active electrode(s) 104 improves the performance of the device. Ofcourse, it will be recognized that mesh electrode 600 may beelectrically insulated from active electrode(s) 104, as in previousembodiments.

[0148] Referring to FIG. 13, another embodiment of the present inventionincorporates an aspiration electrode 160 within an aspiration lumen 162of the probe. As shown, the electrode 160 is positioned just proximal ofdistal opening 209 so that the tissue fragments are ablated as theyenter lumen 162. In the representative embodiment, aspiration electrode160 comprises a loop electrode that extends across the aspiration lumen162. However, it will be recognized that many other configurations arepossible. In this embodiment, the return electrode 164 is locatedtowards the exterior of the shaft, as in the previously describedembodiments. Alternatively, the return electrode(s) may be locatedwithin the aspiration lumen 162 with the aspiration electrode 160. Forexample, the inner insulating coating 163 may be exposed at portionswithin the lumen 162 to provide a conductive path between this exposedportion of return electrode 164 and the aspiration electrode 160. Thelatter embodiment has the advantage of confining the electric currentsto within the aspiration lumen. In addition, in dry fields in which theconductive fluid is delivered to the target site, it is usually easierto maintain a conductive fluid path between the active and returnelectrodes in the latter embodiment because the conductive fluid isaspirated through the aspiration lumen 162 along with the tissuefragments.

[0149] Referring now to FIGS. 14A-14C, an alternative embodimentincorporating a metal screen 610 is illustrated. As shown, metal screen610 has a plurality of peripheral openings 612 for receiving activeelectrodes 104, and a plurality of inner openings 614 for allowingaspiration of fluid and tissue through an opening 609 of the aspirationlumen. As shown, screen 610 is press fitted over active electrodes 104and then adhered to shaft 100 of probe 20/90. Similar to the meshelectrode embodiment, metal screen 610 may comprise a variety ofconductive metals, such as titanium, tantalum, steel, stainless steel,tungsten, copper, gold or the like. In the representative embodiment,metal screen 610 is coupled directly to, or integral with, activeelectrode(s) 104. In this embodiment, the active electrode(s) 104 andthe metal screen 610 are electrically coupled to each other.

[0150]FIGS. 15A to 15D illustrate embodiments of an electrosurgicalprobe 350 specifically designed for the treatment of herniated ordiseased spinal discs. Referring to FIG. 15A, probe 350 comprises anelectrically conductive shaft 352, a handle 354 coupled to the proximalend of shaft 352 and an electrically insulating support member 356 atthe distal end of shaft 352. Probe 350 further includes a shrink wrappedinsulating sleeve 358 over shaft 352, and an exposed portion of shaft352 that functions as the return electrode 360. In the representativeembodiment, probe 350 comprises a plurality of active electrodes 362extending from the distal end of support member 356. As shown, returnelectrode 360 is spaced a further distance from active electrodes 362than in the embodiments described above. In this embodiment, the returnelectrode 360 is spaced a distance of about 2.0 mm to 50 mm, preferablyabout 5 mm to 25 mm from active electrodes 362. In addition, returnelectrode 360 has a larger exposed surface area than in previousembodiments, having a length in the range of about 2.0 mm to 40 mm,preferably about 5 mm to 20 mm. Accordingly, electric current passingfrom active electrodes 362 to return electrode 360 will follow a currentflow path 370 that is further away from shaft 352 than in the previousembodiments. In some applications, this current flow path 370 results ina deeper current penetration into the surrounding tissue with the samevoltage level, and thus increased thermal heating of the tissue. Asdiscussed above, this increased thermal heating may have advantages insome applications of treating disc or other spinal abnormalities.Typically, it is desired to achieve a tissue temperature in the range ofabout 60° C. to 100° C. to a depth of about 0.2 mm to 5 mm, usuallyabout 1 mm to 2 mm. The voltage required for this thermal damage willpartly depend on the electrode configurations, the conductivity of thetissue and the area immediately surrounding the electrodes, the timeperiod in which the voltage is applied and the depth of tissue damagedesired. With the electrode configurations described in FIGS. 15A-15D,the voltage level for thermal heating will usually be in the range ofabout 20 volts rms to 300 volts rms, preferably about 60 volts rms to200 volts rms. The peak-to-peak voltages for thermal heating with asquare wave form having a crest factor of about 2 are typically in therange of about 40 to 600 volts peak-to-peak, preferably about 120 to 400volts peak-to-peak. The higher the voltage is within this range, theless time required. If the voltage is too high, however, the surfacetissue may be vaporized, debulked or ablated, which is undesirable.

[0151] In alternative embodiments, the electrosurgical system used inconjunction with probe 350 may include a dispersive return electrode 450(see FIG. 16) for switching between bipolar and monopolar modes. In thisembodiment, the system will switch between an ablation mode, where thedispersive pad 450 is deactivated and voltage is applied between activeand return electrodes 362, 360, and a subablation or thermal heatingmode, where the active electrode(s) 362 are deactivated and voltage isapplied between the dispersive pad 450 and the return electrode 360. Inthe subablation mode, a lower voltage is typically applied and thereturn electrode 360 functions as the active electrode to providethermal heating and/or coagulation of tissue surrounding returnelectrode 360.

[0152]FIG. 15B illustrates yet another embodiment of the presentinvention. As shown, electrosurgical probe 350 comprises an electrodeassembly 372 having one or more active electrode(s) 362 and a proximallyspaced return electrode 360 as in previous embodiments. Return electrode360 is typically spaced about 0.5 mm to 25 mm, preferably 1.0 mm to 5.0mm from the active electrode(s) 362, and has an exposed length of about1 mm to 20 mm. In addition, electrode assembly 372 includes twoadditional electrodes 374, 376 spaced axially on either side of returnelectrode 360. Electrodes 374, 376 are typically spaced about 0.5 mm to25 mm, preferably about 1 mm to 5 mm from return electrode 360. In therepresentative embodiment, the additional electrodes 374, 376 areexposed portions of shaft 352, and the return electrode 360 iselectrically insulated from shaft 352 such that a voltage difference maybe applied between electrodes 374, 376 and electrode 360. In thisembodiment, probe 350 may be used in at least two different modes, anablation mode and a subablation or thermal heating mode. In the ablationmode, voltage is applied between active electrode(s) 362 and returnelectrode 360 in the presence of electrically conductive fluid, asdescribed above. In the ablation mode, electrodes 374, 376 aredeactivated. In the thermal heating or coagulation mode, activeelectrode(s) 362 are deactivated and a voltage difference is appliedbetween electrodes 374, 376 and electrode 360 such that a high frequencycurrent 370 flows therebetween, as shown in FIG. 15B. In the thermalheating mode, a lower voltage is typically applied below the thresholdfor plasma formation and ablation, but sufficient to cause some thermaldamage to the tissue immediately surrounding the electrodes withoutvaporizing or otherwise debulking this tissue so that the current 370provides thermal heating and/or coagulation of tissue surroundingelectrodes 360, 372, 374.

[0153]FIG. 15C illustrates another embodiment of probe 350 incorporatingan electrode assembly 372 having one or more active electrode(s) 362 anda proximally spaced return electrode 360 as in previous embodiments.Return electrode 360 is typically spaced about 0.5 mm to 25 mm,preferably 1.0 mm to 5.0 mm from the active electrode(s) 362, and has anexposed length of about 1 mm to 20 mm. In addition, electrode assembly372 includes a second active electrode 380 separated from returnelectrode 360 by an electrically insulating spacer 382. In thisembodiment, handle 354 includes a switch 384 for toggling probe 350between at least two different modes, an ablation mode and a subablationor thermal heating mode. In the ablation mode, voltage is appliedbetween active electrode(s) 362 and return electrode 360 in the presenceof electrically conductive fluid, as described above. In the ablationmode, electrode 380 is deactivated. In the thermal heating orcoagulation mode, active electrode(s) 362 may be deactivated and avoltage difference is applied between electrode 380 and electrode 360such that a high frequency current 370 flows therebetween.Alternatively, active electrode(s) 362 may not be deactivated as thehigher resistance of the smaller electrodes may automatically send theelectric current to electrode 380 without having to physically decoupleelectrode(s) 362 from the circuit. In the thermal heating mode, a lowervoltage is typically applied below the threshold for plasma formationand ablation, but sufficient to cause some thermal damage to the tissueimmediately surrounding the electrodes without vaporizing or otherwisedebulking this tissue so that the current 370 provides thermal heatingand/or coagulation of tissue surrounding electrodes 360, 380.

[0154] Of course, it will be recognized that a variety of otherembodiments may be used to accomplish similar functions as theembodiments described above. For example, electrosurgical probe 350 mayinclude a plurality of helical bands formed around shaft 352, with oneor more of the helical bands having an electrode coupled to the portionof the band such that one or more electrodes are formed on shaft 352spaced axially from each other.

[0155]FIG. 15D illustrates another embodiment of the invention designedfor channeling through tissue and creating lesions therein to treatspinal discs and/or snoring and sleep apnea. As shown, probe 350 issimilar to the probe in FIG. 15C having a return electrode 360 and athird, coagulation electrode 380 spaced proximally from the returnelectrode 360. In this embodiment, active electrode 362 comprises asingle electrode wire extending distally from insulating support member356. Of course, the active electrode 362 may have a variety ofconfigurations to increase the current densities on its surfaces, e.g.,a conical shape tapering to a distal point, a hollow cylinder, loopelectrode and the like. In the representative embodiment, supportmembers 356 and 382 are constructed of a material, such as ceramic,glass, silicone and the like. The proximal support member 382 may alsocomprise a more conventional organic material as this support member 382will generally not be in the presence of a plasma that would otherwiseetch or wear away an organic material.

[0156] The probe 350 in FIG. 15D does not include a switching element.In this embodiment, all three electrodes are activated when the powersupply is activated. The return electrode 360 has an opposite polarityfrom the active and coagulation electrodes 362, 380 such that current370 flows from the latter electrodes to the return electrode 360 asshown. In the preferred embodiment, the electrosurgical system includesa voltage reduction element or a voltage reduction circuit for reducingthe voltage applied between the coagulation electrode 380 and returnelectrode 360. The voltage reduction element allows the power supply 28to, in effect, apply two different voltages simultaneously to twodifferent electrodes. Thus, for channeling through tissue, the operatormay apply a voltage sufficient to provide ablation of the tissue at thetip of the probe (i.e., tissue adjacent to the active electrode 362). Atthe same time, the voltage applied to the coagulation electrode 380 willbe insufficient to ablate tissue. For thermal heating or coagulation oftissue, for example, the voltage reduction element will serve to reducea voltage of about 100 volts rms to 300 volts rms to about 45 volts rmsto 90 volts rms, which is a suitable voltage for coagulation of tissuewithout ablation (e.g., molecular dissociation) of the tissue.

[0157] In the representative embodiment, the voltage reduction elementcomprises a pair of capacitors forming a bridge divider(not shown)coupled to the power supply and coagulation electrode 380. Thecapacitors usually have a capacitance of about 200 pF to 500 pF (at 500volts) and preferably about 300 pF to 350 pF (at 500 volts). Of course,the capacitors may be located in other places within the system, such asin, or distributed along the length of, the cable, the generator, theconnector, etc. In addition, it will be recognized that other voltagereduction elements, such as diodes, transistors, inductors, resistors,capacitors or combinations thereof, may be used in conjunction with thepresent invention. For example, the probe 350 may include a codedresistor (not shown) that is constructed to lower the voltage appliedbetween the return and coagulation electrodes 360, 380, respectively. Inaddition, electrical circuits may be employed for this purpose.

[0158] Of course, for some procedures, the probe will typically notrequire a voltage reduction element. Alternatively, the probe mayinclude a voltage increasing element or circuit, if desired.Alternatively or additionally, cable 22/34 that couples power supply 28to the probe 90 may be used as a voltage reduction element. The cablehas an inherent capacitance that can be used to reduce the power supplyvoltage if the cable is placed into the electrical circuit between thepower supply, the active electrodes and the return electrode. In thisembodiment, cable 22/34 may be used alone, or in combination with one ofthe voltage reduction elements discussed above, e.g., a capacitor.Further, it should be noted that the present invention can be used witha power supply that is adapted to apply two different voltages withinthe selected range for treatment of tissue. In this embodiment, avoltage reduction element or circuitry may not be desired.

[0159] In one specific embodiment, the probe 350 is manufactured byfirst inserting an electrode wire (active electrode 362) through aceramic tube (insulating member 356) such that a distal portion of thewire extends through the distal portion of the tube, and bonding thewire to the tube, typically with an appropriate epoxy. A stainless steeltube (return electrode 360) is then placed over the proximal portion ofthe ceramic tube, and a wire (e.g., nickel wire) is bonded, typically byspot welding, to the inside surface of the stainless steel tube. Thestainless steel tube is coupled to the ceramic tube by epoxy, and thedevice is cured in an oven or other suitable heat source. A secondceramic tube (insulating member 382) is then placed inside of theproximal portion of the stainless steel tube, and bonded in a similarmanner. The shaft 358 is then bonded to the proximal portion of thesecond ceramic tube, and an insulating sleeve (e.g. polyimide) iswrapped around shaft 358 such that only a distal portion of the shaft isexposed (i.e., coagulation electrode 380). The nickel wire connectionwill extend through the center of shaft 358 to connect return electrode360 to the power supply. The active electrode 362 may form a distalportion of shaft 358, or it may also have a connector extending throughshaft 358 to the power supply.

[0160] In use, the physician positions active electrode 362 adjacent tothe tissue surface to be treated (i.e., a spinal disc). The power supplyis activated to provide an ablation voltage between active and returnelectrodes 362, 360, respectively, and a coagulation or thermal heatingvoltage between coagulation and return electrodes 380, 360,respectively. An electrically conductive fluid can then be providedaround active electrode 362, and in the junction between the active andreturn electrodes 360, 362 to provide a current flow path therebetween.This may be accomplished in a variety of manners, as discussed above.The active electrode 362 is then advanced through the space left by theablated tissue to form a channel in the disc. During ablation, theelectric current between the coagulation and return electrode istypically insufficient to cause any damage to the surface of the tissueas these electrodes pass through the tissue surface into the channelcreated by active electrode 362. Once the physician has formed thechannel to the appropriate depth, he or she will cease advancement ofthe active electrode, and will either hold the instrument in place forapproximately 5 seconds to 30 seconds, or can immediately remove thedistal tip of the instrument from the channel (see detailed discussionof this below). In either event, when the active electrode is no longeradvancing, it will eventually stop ablating tissue.

[0161] Prior to entering the channel formed by the active electrode 362,an open circuit exists between return and coagulation electrodes 360,380. Once coagulation electrode 380 enters this channel, electriccurrent will flow from coagulation electrode 380, through the tissuesurrounding the channel, to return electrode 360. This electric currentwill heat the tissue immediately surrounding the channel to coagulateany severed vessels at the surface of the channel. If the physiciandesires, the instrument may be held within the channel for a period oftime to create a lesion around the channel, as discussed in more detailbelow.

[0162]FIG. 16 illustrates yet another embodiment of an electrosurgicalsystem 440 incorporating a dispersive return pad 450 attached to theelectrosurgical probe 400. In this embodiment, the invention functionsin the bipolar mode as described above. In addition, the system 440 mayfunction in a monopolar mode in which a high frequency voltagedifference is applied between the active electrode(s) 410, and thedispersive return pad 450. In the exemplary embodiment, the pad 450 andthe probe 400 are coupled together, and are both disposable, single-useitems. The pad 450 includes an electrical connector 452 that extendsinto handle 404 of probe 400 for direct connection to the power supply.Of course, the invention would also be operable with a standard returnpad that connects directly to the power supply. In this embodiment, thepower supply 460 will include a switch, e.g., a foot pedal 462, forswitching between the monopolar and bipolar modes. In the bipolar mode,the return path on the power supply is coupled to return electrode 408on probe 400, as described above. In the monopolar mode, the return pathon the power supply is coupled to connector 452 of pad 450, activeelectrode(s) 410 are decoupled from the electrical circuit, and returnelectrode 408 functions as the active electrode. This allows the surgeonto switch between bipolar and monopolar modes during, or prior to, thesurgical procedure. In some cases, it may be desirable to operate in themonopolar mode to provide deeper current penetration and, thus, agreater thermal heating of the tissue surrounding the return electrodes.In other cases, such as ablation of tissue, the bipolar modality may bepreferable to limit the current penetration to the tissue.

[0163] In one configuration, the dispersive return pad 450 is adaptedfor coupling to an external surface of the patient in a regionsubstantially close to the target region. For example, during thetreatment of tissue in the head and neck, the dispersive return pad isdesigned and constructed for placement in or around the patient'sshoulder, upper back or upper chest region. This design limits thecurrent path through the patient's body to the head and neck area, whichminimizes the damage that may be generated by unwanted current paths inthe patient's body, particularly by limiting current flow through thepatient's heart. The return pad is also designed to minimize the currentdensities at the pad, to thereby minimize patient skin burns in theregion where the pad is attached.

[0164] Referring to FIG. 17, the electrosurgical system according to thepresent invention may also be configured as a catheter system 400. Asshown in FIG. 17, a catheter system 400 generally comprises anelectrosurgical catheter 460 connected to a power supply 28 by aninterconnecting cable 486 for providing high frequency voltage to atarget tissue and an irrigant reservoir or source 600 for providingelectrically conductive fluid to the target site. Catheter 460 generallycomprises an elongate, flexible shaft body 462 including a tissueremoving or ablating region 464 at the distal end of body 462. Theproximal portion of catheter 460 includes a multi-lumen fitment 614which provides for interconnections between lumens and electrical leadswithin catheter 460 and conduits and cables proximal to fitment 614. Byway of example, a catheter electrical connector 496 is removablyconnected to a distal cable connector 494 which, in turn, is removablyconnectable to generator 28 through connector 492. One or moreelectrically conducting lead wires (not shown) within catheter 460extend between one or more active electrodes 463 and a coagulationelectrode 467 at tissue ablating region 464 and one or morecorresponding electrical terminals (also not shown) in catheterconnector 496 via active electrode cable branch 487. Similarly, a returnelectrode 466 at tissue ablating region 464 is coupled to a returnelectrode cable branch 489 of catheter connector 496 by lead wires (notshown). Of course, a single cable branch (not shown) may be used forboth active and return electrodes.

[0165] Catheter body 462 may include reinforcing fibers or braids (notshown) in the walls of at least the distal ablation region 464 of body462 to provide responsive torque control for rotation of activeelectrodes during tissue engagement. This rigid portion of the catheterbody 462 preferably extends only about 7 mm to 10 mm while the remainderof the catheter body 462 is flexible to provide good trackability duringadvancement and positioning of the electrodes adjacent target tissue.

[0166] In some embodiments, conductive fluid 50 is provided to tissueablation region 464 of catheter 460 via a lumen (not shown in FIG. 17)within catheter 460. Fluid is supplied to the lumen from the sourcealong a conductive fluid supply line 602 and a conduit 603, which iscoupled to the inner catheter lumen at multi-lumen fitment 614. Thesource of conductive fluid (e.g., isotonic saline) may be an irrigantpump system (not shown) or a gravity-driven supply, such as an irrigantreservoir 600 positioned several feet above the level of the patient andtissue ablating region. A control valve 604 may be positioned at theinterface of fluid supply line 602 and conduit 603 to allow manualcontrol of the flow rate of electrically conductive fluid 50.Alternatively, a metering pump or flow regulator may be used toprecisely control the flow rate of the conductive fluid.

[0167] System 400 can further include an aspiration or vacuum system(not shown) to aspirate liquids and gases from the target site. Theaspiration system will usually comprise a source of vacuum coupled tofitment 614 by a aspiration connector 605.

[0168] The present invention is particularly useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. As shown in FIGS. 18-23, a percutaneous penetration270 is made in the patients' back 272 so that the superior lamina 274can be accessed. Typically, a small needle (not shown) is used initiallyto localize the disc space level, and a guidewire (not shown) isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina 274. Sequential cannulated dilators 276 are inserted over theguide wire and each other to provide a hole from the incision 220 to thelamina 274. The first dilator may be used to “palpate” the lamina 274,assuring proper location of its tip between the spinous process andfacet complex just above the inferior edge of the lamina 274. As shownin FIG. 21, a tubular retractor 278 is then passed over the largestdilator down to the lamina 274. The dilators 276 are removed,establishing an operating corridor within the tubular retractor 278.

[0169] As shown in FIG. 19, an endoscope 280 is then inserted into thetubular retractor 278 and a ring clamp 282 is used to secure theendoscope 280. Typically, the formation of the operating corridor withinretractor 278 requires the removal of soft tissue, muscle or other typesof tissue that were forced into this corridor as the dilators 276 andretractor 278 were advanced down to the lamina 274. This tissue isusually removed with mechanical instruments, such as pituitary rongeurs,curettes, graspers, cutters, drills, microdebriders, and the like.Unfortunately, these mechanical instruments greatly lengthen andincrease the complexity of the procedure. In addition, these instrumentssever blood vessels within this tissue, usually causing profuse bleedingthat obstructs the surgeon's view of the target site.

[0170] According to another aspect of the present invention, anelectrosurgical probe or catheter 284 as described above is introducedinto the operating corridor within the retractor 278 to remove the softtissue, muscle and other obstructions from this corridor so that thesurgeon can easily access and visualization the lamina 274. Once thesurgeon has introduced the probe 284, electrically conductive fluid 285can be delivered through tube 233 and opening 237 to the tissue (seeFIG. 4). The fluid flows past the return electrode 112 to the activeelectrodes 104 at the distal end of the shaft. The rate of fluid flow iscontrolled with valve 17 (FIG. 1) such that the zone between the tissueand electrode support 102 is constantly immersed in the fluid. The powersupply 28 is then turned on and adjusted such that a high frequencyvoltage difference is applied between active electrodes 104 and returnelectrode 112. The electrically conductive fluid provides the conductionpath (see current flux lines) between active electrodes 104 and thereturn electrode 112.

[0171] The high frequency voltage is sufficient to convert theelectrically conductive fluid (not shown) between the target tissue andactive electrode(s) 104 into an ionized vapor layer or plasma (notshown). As a result of the applied voltage difference between activeelectrode(s) 104 and the target tissue (i.e., the voltage gradientacross the plasma layer), charged particles in the plasma (viz.,electrons) are accelerated towards the tissue. At sufficiently highvoltage differences, these charged particles gain sufficient energy tocause dissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles within thetissue confines the molecular dissociation process to the surface layerto minimize damage and necrosis to the underlying tissue.

[0172] During the process, the gases will be aspirated through opening209 and suction tube 211 to a vacuum source. In addition, excesselectrically conductive fluid, and other fluids (e.g., blood) will beaspirated from the operating corridor to facilitate the surgeon's view.During ablation of the tissue, the residual heat generated by thecurrent flux lines (typically less than 150° C.), will usually besufficient to coagulate any severed blood vessels at the site. If not,the surgeon may switch the power supply 28 into the coagulation mode bylowering the voltage to a level below the threshold for fluidvaporization, as discussed above. This simultaneous hemostasis resultsin less bleeding and facilitates the surgeon's ability to perform theprocedure.

[0173] Another advantage of the present invention is the ability toprecisely ablate soft tissue without causing necrosis or thermal damageto the underlying and surrounding tissues, nerves or bone. In addition,the voltage can be controlled so that the energy directed to the targetsite is insufficient to ablate the lamina 274 so that the surgeon canliterally clean the tissue off the lamina 274, without ablating orotherwise effecting significant damage to the lamina.

[0174] Referring now to FIGS. 20 and 21, once the operating corridor issufficiently cleared, a laminotomy and medial facetectomy isaccomplished either with conventional techniques (e.g., Kerrison punchor a high speed drill) or with the electrosurgical probe 284 asdiscussed above. After the nerve root is identified, medical retractioncan be achieved with a retractor 288, or the present invention can beused to precisely ablate the disc. If necessary, epidural veins arecauterized either automatically or with the coagulation mode of thepresent invention. If an annulotomy is necessary, it can be accomplishedwith a microknife or the ablation mechanism of the present inventionwhile protecting the nerve root with the retractor 288. The herniateddisc 290 is then removed with a pituitary rongeur in a standard fashion,or once again through ablation as described above.

[0175] In another embodiment, the present invention involves achanneling technique in which small holes or channels are formed withinthe disc 290, and thermal energy is applied to the tissue surfaceimmediately surrounding these holes or channels to cause thermal damageto the tissue surface, thereby stiffening and debulking the surroundingtissue structure of the disc. Applicant has discovered that suchstiffening of the tissue structure in the disc helps to reduce thepressure applied against the spinal nerves by the disc, therebyrelieving back and neck pain.

[0176] As shown in FIG. 21, the electrosurgical instrument 350 isintroduced to the target site at the disc 290 as described above, or inanother percutaneous manner (see FIGS. 23-25 below). The electrodeassembly 351 is positioned adjacent to or against the disc surface, andelectrically conductive fluid is delivered to the target site, asdescribed above. Alternatively, the conductive fluid is applied to thetarget site, or the distal end of probe 350 is dipped into conductivefluid or gel prior to introducing the probe 350 into the patient. Thepower supply 28 is then activated and adjusted such that a highfrequency voltage difference is applied to the electrode assembly asdescribed above.

[0177] Depending on the procedure, the surgeon may translate orotherwise move the electrodes relative to the target disc tissue to formholes, channels, stripes, divots, craters or the like within the disc.In addition, the surgeon may purposely create some thermal damage withinthese holes, or channels to form scar tissue that will stiffen anddebulk the disc. In one embodiment, the physician axially translates theelectrode assembly 351 into the disc tissue as the tissue isvolumetrically removed to form one or more holes 702 therein (see alsoFIG. 22). The holes 702 will typically have a diameter of less than 2mm, preferably less than 1 mm. In another embodiment (not shown), thephysician translates the active electrode across the outer surface ofthe disc to form one or more channels or troughs. Applicant has foundthat the present invention can quickly and cleanly create such holes,divots or channels in tissue with the cold ablation technology describedherein. A more complete description of methods for forming holes orchannels in tissue can be found in U.S. Pat. No. 5,683,366, the completedisclosure of which is incorporated herein by reference for allpurposes.

[0178]FIG. 22 is a more detailed viewed of the probe 350 of FIG. 15Dforming a hole 702 in a disc 290. Hole 702 is preferably formed with themethods described in detail above. Namely, a high frequency voltagedifference is applied between active and return electrodes 362, 360,respectively, in the presence of an electrically conductive fluid suchthat an electric current 361 passes from the active electrode 362,through the conductive fluid, to the return electrode 360. As shown inFIG. 22, this will result in shallow or no current penetration into thedisc tissue 704. The fluid may be delivered to the target site, applieddirectly to the target site, or the distal end of the probe may bedipped into the fluid prior to the procedure. The voltage is sufficientto vaporize the fluid around active electrode 362 to form a plasma withsufficient energy to effect molecular dissociation of the tissue. Thedistal end of probe 350 is then axially advanced through the tissue asthe tissue is removed by the plasma in front of the probe 350. The holes702 will typically have a depth D in the range of about 0.5 cm to 2.5cm, preferably about 1.2 cm to 1.8 cm, and a diameter d of about 0.5 mmto 5 mm, preferably about 1.0 mm to 3.0 mm. The exact diameter will, ofcourse, depend on the diameter of the electrosurgical probe used for theprocedure.

[0179] During the formation of each hole 702, the conductive fluidbetween active and return electrodes 362, 360 will generally minimizecurrent flow into the surrounding tissue, thereby minimizing thermaldamage to the tissue. Therefore, severed blood vessels on the surface705 of the hole 702 may not be coagulated as the electrodes 362 advancethrough the tissue. In addition, in some procedures, it may be desiredto thermally damage the surface 705 of the hole 702 to stiffen thetissue. For these reasons, it may be desired in some procedures toincrease the thermal damage caused to the tissue surrounding hole 702.In the embodiment shown in FIG. 15D, it may be necessary to either: (1)withdraw the probe 350 slowly from hole 702 after coagulation electrode380 has at least partially advanced past the outer surface of the disctissue 704 into the hole 702 (as shown in FIG. 22); or (2) hold theprobe 350 within the hole 702 for a period of time, e.g., on the orderof 1 seconds to 30 seconds. Once the coagulation electrode is in contactwith, or adjacent to, tissue, electric current 755 flows through thetissue surrounding hole 702 and creates thermal damage therein. Thecoagulation and return electrodes 380, 360 both have relatively large,smooth exposed surfaces to minimize high current densities at theirsurfaces, which minimizes damage to the surface 705 of hole. Meanwhile,the size and spacing of these electrodes 360, 380 allows for relativelydeep current penetration into the tissue 704. In the representativeembodiment, the thermal necrosis (not shown) will extend about 1.0 mm to5.0 mm from surface 705 of hole 702. In this embodiment, the probe mayinclude one or more temperature sensors (not shown) on probe coupled toone or more temperature displays on the power supply 28 such that thephysician is aware of the temperature within the hole 702 during theprocedure.

[0180] In other embodiments, the physician switches the electrosurgicalsystem from the ablation mode to the subablation or thermal heating modeafter the hole 702 has been formed. This is typically accomplished bypressing a switch or foot pedal to reduce the voltage applied to a levelbelow the threshold required for ablation for the particular electrodeconfiguration and the conductive fluid being used in the procedure (asdescribed above). In the subablation mode, the physician will thenremove the distal end of the probe 350 from the hole 702. As the probeis withdrawn, high frequency current flows from the active electrodes362 through the surrounding tissue to the return electrode 360. Thiscurrent flow heats the tissue and coagulates severed blood vessels atsurface 705.

[0181] In another embodiment, the electrosurgical probe of the presentinvention can be used to ablate and/or contract soft tissue within thedisc 290 to allow the annulus fibrosus 292 to repair itself to preventreoccurrence of this procedure. For tissue contraction, a sufficientvoltage difference is applied between the active electrodes 104 and thereturn electrode 112 to elevate the tissue temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from 60° C. to 70° C. This temperatureelevation causes contraction of the collagen connective fibers withinthe disc tissue so that the nucleus pulposus withdraws into the annulusfibrosus 292.

[0182] In one method of tissue contraction according to the presentinvention, an electrically conductive fluid is delivered to the targetsite as described above, and heated to a sufficient temperature toinduce contraction or shrinkage of the collagen fibers in the targettissue. The electrically conductive fluid is heated to a temperaturesufficient to substantially irreversibly contract the collagen fibers,which generally requires a tissue temperature in the range of about 45°C. to 90° C., usually about 60° C. to 70° C. The fluid is heated byapplying high frequency electrical energy to the active electrode(s) incontact with the electrically conductive fluid. The current emanatingfrom the active electrode(s) 104 heats the fluid and generates a jet orplume of heated fluid, which is directed towards the target tissue. Theheated fluid elevates the temperature of the collagen sufficiently tocause hydrothermal shrinkage of the collagen fibers. The returnelectrode 112 draws the electric current away from the tissue site tolimit the depth of penetration of the current into the tissue, therebyinhibiting molecular dissociation and breakdown of the collagen tissueand minimizing or completely avoiding damage to surrounding andunderlying tissue structures beyond the target tissue site. In anexemplary embodiment, the active electrode(s) 104 are held away from thetissue a sufficient distance such that the RF current does not pass intothe tissue at all, but rather passes through the electrically conductivefluid back to the return electrode. In this embodiment, the primarymechanism for imparting energy to the tissue is the heated fluid, ratherthan the electric current.

[0183] In an alternative embodiment, the active electrode(s) 104 arebrought into contact with, or close proximity to, the target tissue sothat the electric current passes directly into the tissue to a selecteddepth. In this embodiment, the return electrode draws the electriccurrent away from the tissue site to limit its depth of 5 penetrationinto the tissue. Applicant has discovered that the depth of currentpenetration also can be varied with the electrosurgical system of thepresent invention by changing the frequency of the voltage applied tothe active electrode and the return electrode. This is because theelectrical impedance of tissue is known to decrease with increasingfrequency due to the electrical properties of cell membranes which 10surround electrically conductive cellular fluid. At lower frequencies(e.g., less than 350 kHz), the higher tissue impedance, the presence ofthe return electrode and the active electrode configuration of thepresent invention (discussed in detail below) cause the current fluxlines to penetrate less deeply resulting in a smaller depth of tissueheating. In an exemplary embodiment, an operating frequency of about 10015 kHz to 200 kHz is applied to the active electrode(s) to obtainshallow depths of collagen shrinkage (e.g., usually less than 1.5 mm andpreferably less than 0.5 mm).

[0184] In another aspect of the invention, the size (e.g., diameter orprincipal dimension) of the active electrodes employed for treating thetissue are selected according to the intended depth of tissue treatment.As described previously in copending patent application PCTInternational Application, U.S. National Phase Serial No.PCT/US94/05168, the depth of current penetration into tissue increaseswith increasing dimensions of an individual active electrode (assumingother factors remain constant, such as the frequency of the electriccurrent, the return electrode configuration, etc.). The depth of currentpenetration (which refers to the depth at which the current density issufficient to effect a change in the tissue, such as collagen shrinkage,irreversible necrosis, etc.) is on the order of the active electrodediameter for the bipolar configuration of the present invention andoperating at a frequency of about 100 kHz to about 200 kHz. Accordingly,for applications requiring a smaller depth of current penetration, oneor more active electrodes of smaller dimensions would be selected.Conversely, for applications requiring a greater depth of currentpenetration, one or more active electrodes of larger dimensions would beselected.

[0185] FIGS. 23-25 illustrate another system and method for treatingswollen or herniated spinal discs according to the present invention. Inthis procedure, an electrosurgical probe 800 comprises a long, thinneedle-like shaft 802 (e.g., on the order of about 1 mm in diameter orless) that can be percutaneously introduced posteriorly through thepatient's back directly into the spine. The shaft 802 may or may not beflexible, depending on the method of access chosen by the physician. Theprobe shaft 802 will include one or more active electrode(s) 804 forapplying electrical energy to tissues within the spine. The probe 800may include one or more return electrode(s) 806, or the return electrodemay be positioned on the patient's back, as a dispersive pad (notshown). As discussed below, however, a bipolar design is preferable.

[0186] As shown in FIG. 23, the distal portion of shaft 802 isintroduced anteriorly through a small percutaneous penetration into theannulus fibrosus 292 of the target spinal disc. To facilitate thisprocess, the distal end of shaft 802 may taper down to a sharper point(e.g., a needle), which can then be retracted to expose activeelectrode(s) 804. Alternatively, the electrodes may be formed around thesurface of the tapered distal portion of shaft (not shown). In eitherembodiment, the distal end of shaft is delivered through the annulus 292to the target nucleus pulposus 294, which may be herniated, extruded,non-extruded, or simply swollen. As shown in FIG. 24, high frequencyvoltage is applied between active electrode(s) 804 and returnelectrode(s) 806 to heat the surrounding collagen to suitabletemperatures for contraction (i.e., typically about 55° C. to about 70°C.). As discussed above, this procedure may be accomplished with amonopolar configuration, as well. However, applicant has found that thebipolar configuration shown in FIGS. 23-25 provides enhanced control ofthe high frequency current, which reduces the risk of spinal nervedamage.

[0187] As shown in FIGS. 24 and 25, once the nucleus pulposus 294 hasbeen sufficiently contracted to retract from impingement on the nerve720, the probe 800 is removed from the target site. In therepresentative embodiment, the high frequency voltage is applied betweenactive and return electrode(s) 804, 806 as the probe is withdrawnthrough the annulus 292. This voltage is sufficient to cause contractionof the collagen fibers within the annulus 292, which allows the annulus292 to contract around the hole formed by probe 800, thereby improvingthe healing of this hole. Thus, the probe 800 seals its own passage asit is withdrawn from the disc.

[0188]FIG. 26A is a side view of an electrosurgical probe 900, accordingto one embodiment of the invention. Probe 900 includes a shaft 902having a distal end portion 902 a and a proximal end portion 902 b. Anactive electrode 910 is disposed on distal end portion 902 a. Althoughonly one active electrode is shown in FIG. 26A, embodiments including aplurality of active electrodes are also within the scope of theinvention. Probe 900 further includes a handle 904 which houses aconnection block 906 for coupling electrodes, e.g. active electrode 910,thereto. Connection block 906 includes a plurality of pins 908 adaptedfor coupling probe 900 to a power supply unit, e.g. power supply 28(FIG. 1).

[0189]FIG. 26B is a side view of the distal end portion of theelectrosurgical probe of FIG. 26A, showing details of shaft distal endportion 902 a. Distal end portion 902 a includes an insulating collar orspacer 916 proximal to active electrode 910, and a return electrode 918proximal to collar 916. A first insulating sleeve (FIG. 28B) may belocated beneath return electrode 918. A second insulating jacket orsleeve 920 may extend proximally from return electrode 918. Secondinsulating sleeve 920 serves as an electrical insulator to inhibitcurrent flow into the adjacent tissue. In a currently preferredembodiment, probe 900 further includes a shield 922 extending proximallyfrom second insulating sleeve 920. Shield 922 may be formed from aconductive metal such as stainless steel, and the like. Shield 922functions to decrease the amount of leakage current passing from probe900 to a patient or a user (e.g., surgeon). In particular, shield 922decreases the amount of capacitive coupling between return electrode 918and an introducer needle 928 (FIG. 31A). Typically shield 922 is coupledto an outer floating conductive layer or cable shield (not shown) of acable, e.g. cables 22, 34 (FIG. 1), connecting probe 900 to power supply28. In this way, the capacitor balance of shaft 902 is disturbed. In oneembodiment, shield 922 may be coated with a durable, hard compound suchas titanium nitride. Such a coating has the advantage of providingreduced friction between shield 922 and introducer inner wall 932 asshaft 902 is axially translated within introducer needle 928 (e.g.,FIGS. 31A, 31B).

[0190]FIG. 27A is a side view of an electrosurgical probe 900 showing afirst curve 924 and a second curve 926 located at distal end portion 902a, wherein second curve 926 is proximal to first curve 924. First curve924 and second curve 926 may be separated by a linear (i.e. straight, ornon-curved), or substantially linear, inter-curve portion 925 of shaft902.

[0191]FIG. 27B is a side view of shaft distal end portion 902 a within arepresentative introducer device or needle 928 having an inner diameterD. Shaft distal end portion 902 a includes first curve 924 and secondcurve 926 separated by inter-curve portion 925. In one embodiment, shaftdistal end portion 902 a includes a linear or substantially linearproximal portion 901 extending from proximal end portion 902 b to secondcurve 926, a linear or substantially linear inter-curve portion 925between first and second curves 924, 926, and a linear or substantiallylinear distal portion 909 between first curve 924 and the distal tip ofshaft 902 (the distal tip is represented in FIG. 27B as an electrodehead 911). When shaft distal end portion 902 a is located withinintroducer needle 928, first curve 924 subtends a first angle ∀ to theinner surface of needle 928, and second curve 926 subtends a secondangle ∃ to inner surface 932 of needle 928. (In the situation shown inFIG. 27B, needle inner surface 932 is essentially parallel to thelongitudinal axis of shaft proximal end portion 902 b (FIG. 27A).) Inone embodiment, shaft distal end portion 902 a is designed such that theshaft distal tip occupies a substantially central transverse locationwithin the lumen of introducer needle 928 when shaft distal end portion902 a is translated axially with respect to introducer needle 928. Thus,as shaft distal end portion 902 a is advanced through the distal openingof needle 928 (FIGS. 30B, 31B), and then retracted back into the distalopening, the shaft distal tip will always occupy a transverse locationtowards the center of introducer needle 928 (even though the tip may becurved or biased away from the longitudinal axis of shaft 902 and needle928 upon its advancement past the distal opening of introducer needle928). In one embodiment, shaft distal end portion 902 a is flexible andhas a configuration which requires shaft distal end portion 902 a bedistorted in the region of at least second curve 926 by application of alateral force imposed by inner wall 932 of introducer needle 928 asshaft distal end portion 902 a is introduced or retracted into needle928. In one embodiment, first curve 924 and second curve 926 are in thesame plane relative to the longitudinal axis of shaft 902, and first andsecond curves 924, 926 are in opposite directions.

[0192] The “S-curve” configuration of shaft 902 shown in FIGS. 27A-Callows the distal end or tip of a device to be advanced or retractedthrough needle distal end 928 a and within the lumen of needle 928without the distal end or tip contacting introducer needle 928.Accordingly, this design allows a sensitive or delicate component to belocated at the distal tip of a device, wherein the distal end or tip isadvanced or retracted through a lumen of an introducer instrumentcomprising a relatively hard material (e.g., an introducer needlecomprising stainless steel). This design also allows a component locatedat a distal end or tip of a device to be constructed from a relativelysoft material, and for the component located at the distal end or tip tobe passed through an introducer instrument comprising a hard materialwithout risking damage to the component comprising a relatively softmaterial.

[0193] The “S-curve” design of shaft distal end portion 902 a allows thedistal tip (e.g., electrode head 911) to be advanced and retractedthrough the distal opening of needle 928 while avoiding contact betweenthe distal tip and the edges of the distal opening of needle 928. (If,for example, shaft distal end portion 902 a included only a single curvethe distal tip would ordinarily come into contact with needle distal end928 a as shaft 902 is retracted into the lumen of needle 928.) Inpreferred embodiments, the length L2 of distal portion 909 and the angle∀ between distal portion 909 and needle inner surface 932 928, whenshaft distal end portion 902 a is compressed within needle 928, areselected such that the distal tip is substantially in the center of thelumen of needle 928, as shown in FIG. 27B. Thus, as the length L2increases, the angle ∀ will decrease, and vice versa. The exact valuesof length L2 and angle ∀ will depend on the inner diameter, D of needle928, the inner diameter, d of shaft distal end portion 902 a, and thesize of the shaft distal tip.

[0194] The presence of first and second curves, 924, 926 provides apredefined bias in shaft 902. In addition, in one embodiment shaftdistal end portion 902 a is designed such that at least one of first andsecond curves 924, 926 are compressed to some extent as shaft distal endportion 902 a is retracted into the lumen of needle 928. Accordingly,the angle of at least one of curves 924, 926 may be changed when distalend portion 902 a is advanced out through the distal opening ofintroducer needle 928, as compared with the corresponding angle whenshaft distal end portion is completely retracted within introducerneedle 928. For example, FIG. 27C shows shaft 902 of FIG. 27B free fromintroducer needle 928, wherein first and second curves 924, 926 areallowed to adopt their natural or uncompressed angles ∀′ and ∃′,respectively, wherein ∃′ is typically equal to or greater than 3. Angle∀′ may be greater than, equal to, or less than angle ∀. Angle ∃′ issubtended by inter-curve portion 925 and proximal portion 901. Whenshaft distal end portion 902 a is unrestrained by introducer needle 928,proximal portion 901 approximates the longitudinal axis of shaft 902.Angle ∃′ is subtended between linear distal portion 909 and a line drawnparallel to proximal portion 901. Electrode head 911 is omitted fromFIG. 27C for the sake of clarity.

[0195] The principle described above with reference to shaft 902 andintroducer needle 928 may equally apply to a range of other medicaldevices. That is to say, the “S-curve” configuration of the inventionmay be included as a feature of any medical system or apparatus in whicha medical instrument may be axially translated or passed within anintroducer device. In particular, the principle of the “S-curve”configuration of the invention may be applied to any apparatus whereinit is desired that the distal end of the medical instrument does notcontact or impinge upon the introducer device as the medical instrumentis advanced from or retracted into the introducer device. The introducerdevice may be any apparatus through which a medical instrument ispassed. Such medical systems may include, for example, a catheter, acannula, an endoscope, and the like.

[0196] When shaft 902 is advanced distally through the needle lumen to apoint where second curve 926 is located distal to needle distal end 928a, the shaft distal tip is deflected from the longitudinal axis ofneedle 928. The amount of this deflection is determined by the relativesize of angles ∃′ and ∀′, and the relative lengths of L1 and L2. Theamount of this deflection will in turn determine the size of a channelor lesion (depending on the application) formed in a tissue treated byelectrode head 911 when shaft 902 is rotated circumferentially withrespect to the longitudinal axis of probe 900.

[0197] As a result of the pre-defined bias in shaft 902, shaft distalend portion 902 a will contact a larger volume of tissue than a linearshaft having the same dimensions. In addition, in one embodiment thepre-defined bias of shaft 902 allows the physician to guide or steer thedistal tip of shaft 902 by a combination of axial movement of needledistal end 928 a and the inherent curvature at shaft distal end portion902 a of probe 900.

[0198] Shaft 902 preferably has a length in the range of from about 4 to3 0 cm. In one aspect of the invention, probe 900 is manufactured in arange of sizes having different lengths and/or diameters of shaft 902. Ashaft of appropriate size can then be selected by the surgeon accordingto the body structure or tissue to be treated and the age or size of thepatient. In this way, patients varying in size from small children tolarge adults can be accommodated. Similarly, for a patient of a givensize, a shaft of appropriate size can be selected by the surgeondepending on the organ or tissue to be treated, for example, whether anintervertebral disc to be treated is in the lumbar spine or the cervicalspine. For example, a shaft suitable for treatment of a disc of thecervical spine may be substantially smaller than a shaft for treatmentof a lumbar disc. For treatment of a lumbar disc in an adult, shaft 902is preferably in the range of from about 15 to 25 cm. For treatment of acervical disc, shaft 902 is preferably in the range of from about 4 toabout 15 cm.

[0199] The diameter of shaft 902 is preferably in the range of fromabout 0.5 to about 2.5 mm, and more preferably from about 1 to 1.5 mm.First curve 924 is characterized by a length L1, while second curve 926is characterized by a length L2 (FIG. 27B). Inter-curve portion 925 ischaracterized by a length L3, while shaft 902 extends distally fromfirst curve 924 a length L4. In one embodiment, L2 is greater than L1.Length L1 may be in the range of from about 0.5 to about 5 mm, while L2may be in the range of from about 1 to about 10 mm. Preferably, L3 andL4 are each in the range of from about 1 to 6 mm.

[0200]FIG. 28A is a side view of shaft distal end portion 902 a ofelectrosurgical probe 900 showing a head 911 of active electrode 910(the latter not shown in FIG. 28A), according to one embodiment of theinvention. In this embodiment, electrode head 911 includes an apicalspike 911 a and an equatorial cusp 911 b. Electrode head 911 exhibits anumber of advantages as compared with, for example, an electrosurgicalprobe having a blunt, globular, or substantially spherical activeelectrode. In particular, electrode head 911 provides a high currentdensity at apical spike 911 a and cusp 911 b. In turn, high currentdensity in the vicinity of an active electrode is advantageous in thegeneration of a plasma; and, as is described fully hereinabove,generation of a plasma in the vicinity of an active electrode isfundamental to ablation of tissue with minimal collateral thermal damageaccording to certain embodiments of the instant invention. Electrodehead 911 provides an additional advantage, in that the sharp edges ofcusp 911 b, and more particularly of apical spike 911 a, facilitatemovement and guiding of head 911 into tissue during surgical procedures,as described fully hereinbelow. In contrast, an electrosurgical probehaving a blunt or rounded apical electrode is more likely to follow apath of least resistance, such as a channel which was previously ablatedwithin nucleus pulposus tissue. Although certain embodiments of theinvention depict head 911 as having a single apical spike, other shapesfor the apical portion of active electrode 910 are also within the scopeof the invention.

[0201]FIG. 28B is a longitudinal cross-sectional view of distal endportion 902 a of shaft 902. Apical electrode head 911 is incommunication with a filament 912. Filament 912 typically comprises anelectrically conductive wire encased within a first insulating sleeve914. First insulating sleeve 914 comprises an insulator, such as varioussynthetic polymeric materials. An exemplary material from which firstinsulating sleeve 914 may be constructed is a polyimide. Firstinsulating sleeve 914 may extend the entire length of shaft 902 proximalto head 911. An insulating collar or spacer 916 is disposed on thedistal end of first insulating sleeve 914, adjacent to electrode head911. Collar 916 preferably comprises a material such as a glass, aceramic, or silicone. The exposed portion of first insulating sleeve 914(i.e., the portion proximal to collar 916) is encased within acylindrical return electrode 918. Return electrode 918 may extendproximally the entire length of shaft 902. Return electrode 918 maycomprise an electrically conductive material such as stainless steel,tungsten, platinum or its alloys, titanium or its alloys, molybdenum orits alloys, nickel or its alloys, and the like. A proximal portion ofreturn electrode 918 is encased within a second insulating sleeve 920,so as to provide an exposed band of return electrode 918 located distalto second sleeve 920 and proximal to collar 916. Second sleeve 920provides an insulated portion of shaft 920 which facilitates handling ofprobe 900 by the surgeon during a surgical procedure. A proximal portionof second sleeve 920 is encased within an electrically conductive shield922. Second sleeve 920 and shield 922 may also extend proximally for theentire length of shaft 902.

[0202]FIG. 29 is a side view of shaft distal end portion 902 a ofelectrosurgical probe 900, indicating the position of first and secondcurves 924, 926, respectively. Probe 900 includes head 911, collar 916,return electrode 918, second insulating sleeve 920, and shield 922,generally as described with reference to FIGS. 28A, 28B. In theembodiment of FIG. 29, first curve 924 is located within returnelectrode 918, while second curve 926 is located within shield 922.However, according to various embodiments of the invention, shaft 902may be provided in which one or more curves are present at alternativeor additional locations or components of shaft 902, other than thelocation of first and second curves 924, 926, respectively, shown inFIG. 29.

[0203]FIG. 30A shows distal end portion 902 a of shaft 902 extendeddistally from an introducer needle 928, according to one embodiment ofthe invention. Introducer needle 928 may be used to convenientlyintroduce shaft 902 into tissue, such as the nucleus pulposus of anintervertebral disc. In this embodiment, due to the curvature of shaftdistal end 902 a, when shaft 902 is extended distally beyond introducerneedle 928, head 911 is displaced laterally from the longitudinal axisof introducer needle 928. However, as shown in FIG. 30B, as shaft 902 isretracted into introducer needle 928, head 911 assumes a substantiallycentral transverse location within lumen 930 (see also FIG. 31B) ofintroducer 928. Such re-alignment of head 911 with the longitudinal axisof introducer 928 is achieved by specific design of the curvature ofshaft distal end 902 a, as accomplished by the instant inventors. Inthis manner, contact of various components of shaft distal end 902 a(e.g., electrode head 911, collar 916, return electrode 918) isprevented, thereby not only facilitating extension and retraction ofshaft 902 within introducer 928, but also avoiding a potential source ofdamage to sensitive components of shaft 902.

[0204]FIG. 31A shows a side view of shaft 902 in relation to an innerwall 932 of introducer needle 928 upon extension or retraction ofelectrode head 911 from, or within, introducer needle 928. Shaft 902 islocated within introducer 928 with head 911 adjacent to introducerdistal end 928 a (FIG. 31B). Under these circumstances, curvature ofshaft 902 may cause shaft distal end 902 a to be forced into contactwith introducer inner wall 932, e.g., at a location of second curve 926.Nevertheless, due to the overall curvature of shaft 902, and inparticular the nature and position of first curve 924 (FIGS. 27A-B),head 911 does not contact introducer distal end 928 a.

[0205]FIG. 31B shows an end view of electrode head 911 in relation tointroducer needle 928 at a point during extension or retraction of shaft902, wherein head 911 is adjacent to introducer distal end 928 a (FIGS.30B, 31B). In this situation, head 911 is substantially centrallypositioned within lumen 930 of introducer 928. Therefore, contactbetween head 911 and introducer 928 is avoided, allowing shaft distalend 902 a to be extended and retracted repeatedly without sustaining anydamage to shaft 902.

[0206]FIG. 32A shows shaft proximal end portion 902 b of electrosurgicalprobe 900, wherein shaft 902 includes a plurality of depth markings 903(shown as 903 a-f in FIG. 32A). In other embodiments, other numbers andarrangements of depth markings 903 may be included on shaft 902. Forexample, in certain embodiments, depth markings may be present along theentire length of shield 922, or a single depth marking 903 may bepresent at shaft proximal end portion 902 b. Depth markings serve toindicate to the surgeon the depth of penetration of shaft 902 into apatient's tissue, organ, or body, during a surgical procedure. Depthmarkings 903 may be formed directly in or on shield 922, and maycomprise the same material as shield 922. Alternatively, depth markings903 may be formed from a material other than that of shield 922. Forexample, depth markings may be formed from materials which have adifferent color and/or a different level of radiopacity, as comparedwith material of shield 922. For example, depth markings may comprise ametal, such as tungsten, gold, or platinum oxide (black), having a levelof radiopacity different from that of shield 922. Such depth markingsmay be visualized by the surgeon during a procedure performed underfluoroscopy. In one embodiment, the length of the introducer needle andthe shaft 902 are selected to limit the range of the shaft beyond thedistal tip of the introducer needle.

[0207]FIG. 32B shows a probe 900, wherein shaft 902 includes amechanical stop 905. Preferably, mechanical stop 905 is located at shaftproximal end portion 902 b. Mechanical stop 905 limits the distance towhich shaft distal end 902 a can be advanced through introducer 928 bymaking mechanical contact with a proximal end 928 b of introducer 928.Mechanical stop 905 may be a rigid material or structure affixed to, orintegral with, shaft 902. Mechanical stop 905 also serves to monitor thedepth or distance of advancement of shaft distal end 902 a throughintroducer 928, and the degree of penetration of distal end 902 a into apatient's tissue, organ, or body. In one embodiment, mechanical stop 905is movable on shaft 902, and stop 905 includes a stop adjustment unit907 for adjusting the position of stop 905 and for locking stop 905 at aselected location on shaft 902.

[0208]FIG. 33 illustrates stages in manufacture of an active electrode910 of a shaft 902, according to one embodiment of the presentinvention. Stage 33-I shows an elongated piece of electricallyconductive material 912′, e.g., a metal wire, as is well known in theart. Material 912′ includes a first end 912′a and a second end 912′b.Stage 33-II shows the formation of a globular structure 911′ from firstend 912′a, wherein globular structure 911′ is attached to filament 912.Globular structure 911′ may be conveniently formed by applying heat tofirst end 912′a. Techniques for applying heat to the end of a metal wireare well known in the art. Stage 33-III shows the formation of anelectrode head 911 from globular structure 911′, wherein activeelectrode 910 comprises head 911 and filament 912 attached to head 911.In this particular embodiment, head 911 includes an apical spike 911 aand a substantially equatorial cusp 911 b.

[0209]FIG. 34 schematically represents a series of steps involved in amethod of making a shaft according to one embodiment of the presentinvention, wherein step 1000 involves providing an active electrodehaving a filament, the active electrode including an electrode headattached to the filament. An exemplary active electrode to be providedin step 1000 is an electrode of the type described with reference toFIG. 33. At this stage (step 1000), the filament may be trimmed to anappropriate length for subsequent coupling to a connection block (FIG.26A).

[0210] Step 1002 involves covering or encasing the filament with a firstinsulating sleeve of an electrically insulating material such as asynthetic polymer or plastic, e.g., a polyimide. Preferably, the firstinsulating sleeve extends the entire length of the shaft. Step 1004involves positioning a collar of an electrically insulating material onthe distal end of the first insulating sleeve, wherein the collar islocated adjacent to the electrode head. The collar is preferably amaterial such as a glass, a ceramic, or silicone. Step 1006 involvesplacing a cylindrical return electrode over the first insulating sleeve.Preferably, the return electrode is positioned such that its distal endis contiguous with the proximal end of the collar, and the returnelectrode preferably extends proximally for the entire length of theshaft. The return electrode may be constructed from stainless steel orother non-corrosive, electrically conductive metal.

[0211] According to one embodiment, a metal cylindrical return electrodeis pre-bent to include a curve within its distal region (i.e. the returnelectrode component is bent prior to assembly onto the shaft). As aresult, the shaft assumes a first curve upon placing the returnelectrode over the first insulating sleeve, i.e. the first curve in theshaft results from the bend in the return electrode. Step 1008 involvescovering a portion of the return electrode with a second insulatinglayer or sleeve such that a band of the return electrode is exposeddistal to the distal end of the second insulating sleeve. In oneembodiment, the second insulating sleeve comprises a heat-shrink plasticmaterial which is heated prior to positioning the second insulatingsleeve over the return electrode. According to one embodiment, thesecond insulating sleeve is initially placed over the entire length ofthe shaft, and thereafter the distal end of the second insulating sleeveis cut back to expose an appropriate length of the return electrode.Step 1010 involves encasing a proximal portion of the second insulatingsleeve within a shield of electrically conductive material, such as acylinder of stainless steel or other metal, as previously describedherein.

[0212]FIG. 35 schematically represents a series of steps involved in amethod of making an electrosurgical probe of the present invention,wherein step 1100 involves providing a shaft having at least one activeelectrode and at least one return electrode. An exemplary shaft to beprovided in step 1100 is that prepared according to the method describedhereinabove with reference to FIG. 34, i.e., the shaft includes a firstcurve. Step 1102 involves bending the shaft to form a second curve.Preferably, the second curve is located at the distal end portion of theshaft, but proximal to the first curve. In one embodiment, the secondcurve is greater than the first curve. (Features of both the first curveand second curve have been described hereinabove, e.g., with referenceto FIG. 27B.) Step 1104 involves providing a handle for the probe. Thehandle includes a connection block for electrically coupling theelectrodes thereto. Step 1106 involves coupling the active and returnelectrodes of the shaft to the connection block. The connection blockallows for convenient coupling of the electrosurgical probe to a powersupply (e.g., power supply 28, FIG. 1). Thereafter, step 1108 involvesaffixing the shaft to the handle.

[0213]FIG. 36A schematically represents a normal intervertebral disc 290in relation to the spinal cord 720, the intervertebral disc having anouter annulus fibrosus 292 enclosing an inner nucleus pulposus 294. Thenucleus pulposus is a relatively soft tissue comprising proteins andhaving a relatively high water content, as compared with the harder,more fibrous annulus fibrosus. FIGS. 36B-D each schematically representan intervertebral disc having a disorder which can lead to discogenicpain, for example due to compression of a nerve root by a distortedannulus fibrosus. Thus, FIG. 36B schematically represents anintervertebral disc exhibiting a protrusion of the nucleus pulposus anda concomitant distortion of the annulus fibrosus. The condition depictedin FIG. 36B clearly represents a contained herniation, which can resultin severe and often debilitating pain. FIG. 36C schematically representsan intervertebral disc exhibiting a plurality of fissures within theannulus fibrosus, again with concomitant distortion of the annulusfibrosus. Such annular fissures may be caused by excessive pressureexerted by the nucleus pulposus on the annulus fibrosus. Excessivepressure within the nucleus pulposus tends to intensify disc disordersassociated with the presence of such fissures. FIG. 36D schematicallyrepresents an intervertebral disc exhibiting fragmentation of thenucleus pulposus and a concomitant distortion of the annulus fibrosus.In this situation, over time, errant fragment 294′ of the nucleuspulposus tends to dehydrate and to diminish in size, often leading to adecrease in discogenic pain over an extended period of time (e.g.,several months). For the sake of clarity, each FIGS. 36B, 36C, 36D showsa single disorder. However, in practice more than one of the depicteddisorders may occur in the same disc.

[0214] Many patients suffer from discogenic pain resulting, for example,from conditions of the type depicted in FIGS. 36B-D. However, only asmall percentage of such patients undergo laminotomy or discectomy.Presently, there is a need for interventional treatment for the largegroup of patients who ultimately do not undergo major spinal surgery,but who sustain significant disability due to various disorders orabnormalities of an intervertebral disc. A common disorder ofintervertebral discs is a contained herniation in which the nucleuspulposus does not breach the annulus fibrosus, but a protrusion of thedisc causes compression of the exiting nerve root, leading to radicularpain. Typical symptoms are leg pain compatible with sciatica. Suchradicular pain may be considered as a particular form of discogenicpain. Most commonly, contained herniations leading to radicular pain areassociated with the lumbar spine, and in particular with intervertebraldiscs at either L4-5 or L5-S1. Various disc abnormalities are alsoencountered in the cervical spine. Methods and apparatus of theinvention are applicable to all segments of the spine, including thecervical spine and the lumbar spine.

[0215]FIG. 37 schematically represents shaft 902 of probe 900 insertedwithin a nucleus pulposus of a disc having at least one fissure in theannulus. Shaft 902 may be conveniently inserted within the nucleuspulposus via introducer needle 928 in a minimally invasive percutaneousprocedure. In a preferred embodiment, a disc in the lumbar spine may beaccessed via a posterior lateral approach, although other approaches arepossible and are within the scope of the invention. The preferred lengthand diameter of shaft 902 and introducer needle 928 to be used in aprocedure will depend on a number of factors, including the region ofthe spine (e.g., lumbar, cervical) or other body region to be treated,and the size of the patient. Preferred ranges for shaft 902 are givenelsewhere herein. In one embodiment for treatment of a lumbar disc,introducer needle 928 preferably has a diameter in the range of fromabout 50% to 150% the inside diameter of a 17 Gauge needle. In anembodiment for treatment of a cervical disc, introducer needle 928preferably has a diameter in the range of from about 50% to 150% theinner diameter of a 20 Gauge needle.

[0216] Shaft 902 includes an active electrode 910, as describedhereinabove. Shaft 902 features curvature at distal end 902 a/902′a, forexample, as described with reference to FIGS. 27A-B. By rotating shaft902 through approximately 180°, shaft distal end 902 a can be moved to aposition indicated by the dashed lines and labeled as 902′a. Thereafter,rotation of shaft 902 through an additional 180° defines a substantiallycylindrical three-dimensional space with a proximal conical arearepresented as a hatched area (shown between 902 a and 902′a). Thebi-directional arrow distal to active electrode 910 indicatestranslation of shaft 902 substantially along the longitudinal axis ofshaft 902. By a combination of axial and rotational movement of shaft902, a much larger volume of the nucleus pulposus can be contacted byelectrode 910, as compared with a corresponding probe having a linear(non-curved) shaft. Furthermore, the curved nature of shaft 902 allowsthe surgeon to change the direction of advancement of shaft 902 byappropriate rotation thereof, and to guide shaft distal end 902 a to aparticular target site within the nucleus pulposus.

[0217] It is to be understood that according to certain embodiments ofthe invention, the curvature of shaft 902 is the same, or substantiallythe same, both prior to it being used in a surgical procedure and whileit is performing ablation during a procedure, e.g., within anintervertebral disc. (One apparent exception to this statement, relatesto the stage in a procedure wherein shaft 902 may be transiently“molded” into a somewhat more linear configuration by the constraints ofintroducer inner wall 932 during housing, or passing, of shaft 902within introducer 928.) In contrast, certain prior art devices, andembodiments of the invention to be described hereinbelow (e.g., withreference to FIGS. 43A, 43B), may be linear or lacking a naturallydefined configuration prior to use, and then be steered into a selectedconfiguration during a surgical procedure.

[0218] While shaft distal end 902 a is at or adjacent to a target sitewithin the nucleus pulposus, probe 900 may be used to ablate tissue byapplication of a first high frequency voltage between active electrode910 and return electrode 918 (e.g., FIG. 26B), wherein the volume of thenucleus pulposus is decreased, the pressure exerted by the nucleuspulposus on the annulus fibrosus is decreased, and at least one nerve ornerve root is decompressed. Accordingly, discogenic pain experienced bythe patient may be alleviated. Preferably, application of the first highfrequency voltage results in formation of a plasma in the vicinity ofactive electrode 910, and the plasma causes ablation by breaking downhigh molecular weight disc tissue components (e.g., proteins) into lowmolecular weight gaseous materials. Such low molecular weight gaseousmaterials may be at least partially vented or exhausted from the disc,e.g., by piston action, upon removal of shaft 902 and introducer 928from the disc and the clearance between the introducer 928 and the shaft902. In addition, by-products of tissue ablation may be removed by anaspiration device (not shown in FIG. 37), as is well known in the art.In this manner, the volume and/or mass of the nucleus pulposus may bedecreased.

[0219] In order to initiate and/or maintain a plasma in the vicinity ofactive electrode 910, a quantity of an electrically conductive fluid maybe applied to shaft 902 and/or the tissue to ablated. The electricallyconductive fluid may be applied to shaft 902 and/or to the tissue to beablated, either before or during application of the first high frequencyvoltage. Examples of electrically conductive fluids are saline (e.g.,isotonic saline), and an electrically conductive gel. An electricallyconductive fluid may be applied to the tissue to be ablated before orduring ablation. A fluid delivery unit or device may be a component ofthe electrosurgical probe itself, or may comprise a separate device,e.g., ancillary device 940 (FIG. 41). Alternatively, many body fluidsand/or tissues (e.g., the nucleus pulposus, blood) at the site to beablated are electrically conductive and can participate in initiation ormaintenance of a plasma in the vicinity of the active electrode.

[0220] In one embodiment, after ablation of nucleus pulposus tissue bythe application of the first high frequency voltage and formation of acavity or channel within the nucleus pulposus, a second high frequencyvoltage may be applied between active electrode 910 and return electrode918, wherein application of the second high frequency voltage causescoagulation of nucleus pulposus tissue adjacent to the cavity orchannel. Such coagulation of nucleus pulposus tissue may lead toincreased stiffness, strength, and/or rigidity within certain regions ofthe nucleus pulposus, concomitant with an alleviation of discogenicpain. Furthermore, coagulation of tissues may lead to necrotic tissuewhich is subsequently broken down as part of a natural bodily processand expelled from the body, thereby resulting in de-bulking of the disc.Although FIG. 37 depicts a disc having fissures within the annulusfibrosus, it is to be understood that apparatus and methods of theinvention discussed with reference to FIG. 37 are also applicable totreating other types of disc disorders, including those described withreference to FIGS. 36B, 36D.

[0221]FIG. 38 shows shaft 902 of electrosurgical probe 900 within anintervertebral disc, wherein shaft distal end 902 a is targeted to aspecific site within the disc. In the situation depicted in FIG. 38, thetarget site is occupied by an errant fragment 294′ of nucleus pulposustissue. Shaft distal end 902 may be guided or directed, at least inpart, by appropriate placement of introducer 928, such that activeelectrode 910 is in the vicinity of fragment 294′. Preferably, activeelectrode 910 is adjacent to, or in contact with, fragment 294′.Although FIG. 38 depicts a disc in which a fragment of nucleus pulposusis targeted by shaft 902, the invention described with reference to FIG.38 may also be used for targeting other aberrant structures within anintervertebral disc, including annular fissures and containedherniations. In a currently preferred embodiment, shaft 902 includes atleast one curve (not shown in FIG. 38), and other features describedherein with reference to FIGS. 26A-35, wherein shaft distal end 902 amay be precisely guided by an appropriate combination of axial androtational movement of shaft 902. The procedure illustrated in FIG. 38may be performed generally according to the description presented withreference to FIG. 37. That is, shaft 902 is introduced into the disc viaintroducer 928 in a percutaneous procedure. After shaft distal end 902 ahas been guided to a target site, tissue at or adjacent to that site isablated by application of a first high frequency voltage. Thereafter,depending on the particular condition of the disc being treated, asecond high frequency voltage may optionally be applied in order tolocally coagulate tissue within the disc.

[0222]FIG. 39 schematically represents a series of steps involved in amethod of ablating disc tissue according to the present invention;wherein step 1200 involves advancing an introducer needle towards anintervertebral disc to be treated. The introducer needle has a lumenhaving a diameter greater than the diameter of the shaft distal end,thereby allowing free passage of the shaft distal end through the lumenof the introducer needle. In one embodiment, the introducer needlepreferably has a length in the range of from about 3 cm to about 25 cm,and the lumen of the introducer needle preferably has a diameter in therange of from about 0.5 cm. to about 2.5 mm. Preferably, the lumen ofthe introducer needle has a diameter in the range of from about 105% toabout 500% of the diameter of the shaft distal end. The introducerneedle may be inserted in the intervertebral disc percutaneously, e.g.via a posterior lateral approach. In one embodiment, the introducerneedle may have dimensions similar to those of an epidural needle, thelatter well known in the art.

[0223] Optional step 1202 involves introducing an electricallyconductive fluid, such as saline, into the disc. In one embodiment, inlieu of step 1202, the ablation procedure may rely on the electricalconductivity of the nucleus pulposus itself. Step 1204 involvesinserting the shaft of the electrosurgical probe into the disc, e.g.,via the introducer needle, wherein the distal end portion of the shaftbears an active electrode and a return electrode. In one embodiment, theshaft includes an outer shield, first and second curves at the distalend portion of the shaft, and an electrode head having an apical spike,generally as described with reference to FIGS. 26A-32.

[0224] Step 1206 involves ablating at least a portion of disc tissue byapplication of a first high frequency voltage between the activeelectrode and the return electrode. In particular, ablation of nucleuspulposus tissue according to methods of the invention serves to decreasethe volume of the nucleus pulposus, thereby relieving pressure exertedon the annulus fibrosus, with concomitant decompression of a previouslycompressed nerve root, and alleviation of discogenic pain.

[0225] In one embodiment, the introducer needle is advanced towards theintervertebral disc until it penetrates the annulus fibrosus and entersthe nucleus pulposus. The shaft distal end in introduced into thenucleus pulposus, and a portion of the nucleus pulposus is ablated.These and other stages of the procedure may be performed underfluoroscopy to allow visualization of the relative location of theintroducer needle and shaft relative to the nucleus pulposus of thedisc. Additionally or alternatively, the surgeon may introduce theintroducer needle into the nucleus pulposus from a first side of thedisc, then advance the shaft distal end through the nucleus pulposusuntil resistance to axial translation of the electrosurgical probe isencountered by the surgeon. Such resistance may be interpreted by thesurgeon as the shaft distal end having contacted the annulus fibrosus atthe opposite side of the disc. Then, by use of depth markings on theshaft (FIG. 32A), the surgeon can retract the shaft a defined distancein order to position the shaft distal end at a desired location relativeto the nucleus pulposus. Once the shaft distal end is suitablypositioned, high frequency voltage may be applied to the probe via thepower supply unit.

[0226] After step 1206, optional step 1208 involves coagulating at leasta portion of the disc tissue. In one embodiment, step 1206 results inthe formation of a channel or cavity within the nucleus pulposus.Thereafter, tissue at the surface of the channel may be coagulatedduring step 1208. Coagulation of disc tissue may be performed byapplication of a second high frequency voltage, as describedhereinabove. After step 1206 or step 1208, the shaft may be moved (step1210) such that the shaft distal end contacts fresh tissue of thenucleus pulposus. The shaft may be axially translated (i.e. moved in thedirection of its longitudinal axis), may be rotated about itslongitudinal axis, or may be moved by a combination of axial androtational movement. In the latter case, a substantially spiral path isdefined by the shaft distal end. After step 1210, steps 1206 and 1208may be repeated with respect to the fresh tissue of the nucleus pulposuscontacted by the shaft distal end. Alternatively, after step 1206 orstep 1208, the shaft may be withdrawn from the disc (step 1212). Step1214 involves withdrawing the introducer needle from the disc. In oneembodiment, the shaft and the needle may be withdrawn from the discconcurrently. Withdrawal of the shaft from the disc may facilitateexhaustion of ablation by-products from the disc. Such ablationby-products include low molecular weight gaseous compounds derived frommolecular dissociation of disc tissue components, as describedhereinabove. The above method may be used to treat any disc disorder inwhich Coblation® and or coagulation of disc tissue is indicated,including contained herniations. In one embodiment, an introducer needlemay be introduced generally as described for step 1200, and afluoroscopic fluid may be introduced through the lumen of the introducerneedle for the purpose of visualizing and diagnosing a disc abnormalityor disorder. Thereafter, depending on the diagnosis, a treatmentprocedure may be performed, e.g., according to steps 1202 through 1214,using the same introducer needle as access. In one embodiment, a distalportion, or the entire length, of the introducer needle may have aninsulating coating on its external surface. Such an insulating coatingon the introducer needle may prevent interference between theelectrically conductive introducer needle and electrode(s) on the probe.

[0227] The size of the cavity or channel formed in a tissue by a singlestraight pass of the shaft through the tissue to be ablated is afunction of the diameter of the shaft (e.g., the diameter of the shaftdistal end and active electrode) and the amount of axial translation ofthe shaft. (By a “single straight pass” of the shaft is meant one axialtranslation of the shaft in a distal direction through the tissue, inthe absence of rotation of the shaft about the longitudinal axis of theshaft, with the power from the power supply turned on.) In the case of acurved shaft, according to various embodiments of the instant invention,a larger channel can be formed by rotating the shaft as it is advancedthrough the tissue. The size of a channel formed in a tissue by a singlerotational pass of the shaft through the tissue to be ablated is afunction of the deflection of the shaft, and the amount of rotation ofthe shaft about its longitudinal axis, as well as the diameter of theshaft (e.g., the diameter of the shaft distal end and active electrode)and the amount of axial translation of the shaft. (By a “singlerotational pass” of the shaft is meant one axial translation of theshaft in a distal direction through the tissue, in the presence ofrotation of the shaft about the longitudinal axis of the shaft, with thepower from the power supply turned on.) To a large extent, the diameterof a channel formed during a rotational pass of the shaft through tissuecan be controlled by the amount of rotation of the shaft, wherein the“amount of rotation” encompasses both the rate of rotation (e.g., theangular velocity of the shaft), and the number of degrees through whichthe shaft is rotated (e.g. the number of turns) per unit length of axialmovement. Typically, according to the invention, the amount of axialtranslation per pass (for either a straight pass or a rotational pass)is not limited by the length of the shaft. Instead, the amount of axialtranslation per single pass is preferably determined by the size of thetissue to be ablated. Depending on the size of the disc or other tissueto be treated, and the nature of the treatment, etc., a channel formedby a probe of the instant invention may preferably have a length in therange of from about 2 mm to about 50 mm, and a diameter in the range offrom about 0.5 mm to about 7.5 mm. In comparison, a channel formed by ashaft of the instant invention during a single rotational pass maypreferably have a diameter in the range of from about 1.5 mm to about 25mm.

[0228] A channel formed by a shaft of the instant invention during asingle straight pass may preferably have a volume in the range of fromabout 1 mm³, or less, to about 2,500 mm³. More preferably, a channelformed by a straight pass of a shaft of the instant invention has avolume in the range of from about 10 mm³ to about 2,500 mm³, and morepreferably in the range of from about 50 mm³ to about 2,500 mm³. Incomparison, a channel formed by a shaft of the instant invention duringa single rotational pass typically has a volume from about twice toabout 15 times the volume of a channel of the same length formed duringa single rotational pass, i.e., in the range of from about 2 mm³ toabout 4,000 mm³, more preferably in the range of from about 50 mm³ toabout 2,000 mm³. While not being bound by theory, the reduction involume of a disc having one or more channels therein is a function ofthe total volume of the one or more channels. FIG. 40 schematicallyrepresents a series of steps involved in a method of guiding the distalend of a shaft of an electrosurgical probe to a target site within anintervertebral disc for ablation of specifically targeted disc tissue,wherein steps 1300 and 1302 are analogous to steps 1200 and 1204 of FIG.39. Thereafter step 1304 involves guiding the shaft distal end to adefined region within the disc. The specific target site may bepre-defined as a result of a previous procedure to visualize the discand its abnormality, e.g., via X-ray examination, endoscopically, orfluoroscopically. As an example, a defined target site within a disc maycomprise a fragment of the nucleus pulposus that has migrated within theannulus fibrosus (see, e.g., FIG. 36D ) resulting in discogenic pain.However, guiding the shaft to defined sites associated with other typesof disc disorders are also possible and is within the scope of theinvention.

[0229] Guiding the shaft distal end to the defined target site may beperformed by axial and/or rotational movement of a curved shaft, asdescribed hereinabove. Or the shaft may be steerable, for example, bymeans of a guide wire, as is well known in the art. Guiding the shaftdistal end may be performed during visualization of the location of theshaft relative to the disc, wherein the visualization may be performedendoscopically or via fluoroscopy. Endoscopic examination may employ afiber optic cable (not shown). The fiber optic cable may be integralwith the electrosurgical probe, or be part of a separate instrument(endoscope). Step 1306 involves ablating disc tissue, and is analogousto step 1206 (FIG. 39). Before or during step 1306, an electricallyconductive fluid may be applied to the disc tissue and/or the shaft inorder to provide a path for current flow between active and returnelectrodes on the shaft, and to facilitate and/or maintain a plasma inthe vicinity of the distal end portion of the shaft. After the shaftdistal end has been guided to a target site and tissue at that site hasbeen ablated, the shaft may be moved locally, e.g., within the sameregion of the nucleus pulposus, or to a second defined target sitewithin the same disc. The shaft distal end may be moved as describedherein (e.g., with reference to step 1210, FIG. 39). Or, according to analternative embodiment, the shaft may be steerable, e.g., by techniqueswell known in the art. Steps 1310 and 1312 are analogous to steps 1212and 1214, respectively (described with reference to FIG. 39).

[0230] It is known in the art that epidural steroid injections cantransiently diminish perineural inflammation of an affected nerve root,leading to alleviation of discogenic pain. In one embodiment of theinvention, methods for ablation of disc tissue described hereinabove maybe conveniently performed in conjunction with an epidural steroidinjection. For example, ablation of disc tissue and epidural injectioncould be carried out as part of a single procedure, by the same surgeon,using equipment common to both procedures (e.g. visualizationequipment). Combining Coblation® and epidural injection in a singleprocedure may provide substantial cost-savings to the healthcareindustry, as well as a significant improvement in patient care.

[0231] As alluded to hereinabove, methods and apparatus of the presentinvention can be used to accelerate the healing process ofintervertebral discs having fissures and/or contained herniations. Inone method, the present invention is useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. For example, as described above in relation to FIGS.18-20, a percutaneous penetration can be made in the patient's back sothat the superior lamina can be accessed. Typically, a small needle isused initially to localize the disc space level, and a guide wire isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina. Sequential cannulated dilators can be inserted over theguide wire and each other to provide a hole from the incision to thelamina. The first dilator may be used to “palpate” the lamina, assuringproper location of its tip between the spinous process and facet complexjust above the inferior edge of the lamina. A tubular retractor can thenbe passed over the largest dilator down to the lamina. The dilators canthen be removed, so as to establish an operating corridor within thetubular retractor. It should be appreciated however, that otherconventional or proprietary methods can be used to access the targetintervertebral disc. Once the target intervertebral disc has beenaccessed, an introducer device may be inserted into the intervertebraldisc.

[0232] With reference to FIG. 41, in one embodiment, both introducerneedle 928 and a second or ancillary introducer 938 may be inserted intothe same disc, to allow introduction of an ancillary device 940 into thetarget disc via ancillary introducer 938. Ancillary device 940 maycomprise, for example, a fluid delivery device, a return electrode, anaspiration lumen, a second electrosurgical probe, or an endoscope havingan optical fiber component. Each of introducer needle 928 and ancillaryintroducer 938 may be advanced through the annulus fibrosus until atleast the distal end portion of each introducer 928 and 938, ispositioned within the nucleus pulposus. Thereafter, shaft 902″ ofelectrosurgical probe 900′ may be inserted through at least one ofintroducers 928, 938, to treat the intervertebral disc. Typically, shaft902″ of probe 900′ has an outer diameter no larger than about 7 French(1 Fr:0.33 mm), and preferably between about 6 French and 7 French.

[0233] Prior to inserting electrosurgical probe 900 into theintervertebral disc, an electrically conductive fluid can be deliveredinto the disk via a fluid delivery assembly (e.g., ancillary device 940)in order to facilitate or promote the Coblation® mechanism within thedisc following the application of a high frequency voltage via probe900′. By providing a separate device (940) for fluid delivery, thedimensions of electrosurgical probe 900′ can be kept to a minimum.Furthermore, when the fluid delivery assembly is positioned withinancillary introducer 938, electrically conductive fluid can beconveniently replenished to the interior of the disc at any given timeduring the procedure. Nevertheless, in other embodiments, the fluiddelivery assembly can be physically coupled to electrosurgical probe900′.

[0234] In some methods, a radiopaque contrast solution (not shown) maybe delivered through a fluid delivery assembly so as to allow thesurgeon to visualize the intervertebral disc under fluoroscopy. In someconfigurations, a tracking device 942 can be positioned on shaft distalend portion 902″a. Additionally or alternatively, shaft 902″ can bemarked incrementally, e.g., with depth markings 903, to indicate to thesurgeon how far the active electrode is advanced into the intervertebraldisc. In one embodiment, tracking device 942 includes a radiopaquematerial that can be visualized under fluoroscopy. Such a trackingdevice 942 and depth markings 903 provide the surgeon with means totrack the position of the active electrode 910 relative to a specifictarget site within the disc to which active electrode 910 is to beguided. Such specific target sites may include, for example, an annularfissure, a contained herniation, or a fragment of nucleus pulposus. Thesurgeon can determine the position of the active electrode 910 byobserving the depth markings 903, or by comparing tracking deviceoutput, and a fluoroscopic image of the intervertebral disc to apre-operative fluoroscopic image of the target intervertebral disc.

[0235] In other embodiments, an optical fiber (not shown) can beintroduced into the disc. The optical fiber may be either integral withprobe 900′ or may be introduced as part of an ancillary device 940 viaancillary introducer 938. In this manner, the surgeon can visuallymonitor the interior of the intervertebral disc and the position ofactive electrode 910.

[0236] In addition to monitoring the position of the distal portion ofelectrosurgical probe 900′, the surgeon can also monitor whether theprobe is in Coblation® mode. In most embodiments, power supply 28 (e.g.,FIG. 1) includes a controller having an indicator, such as a light, anaudible sound, or a liquid crystal display (LCD), to indicate whetherprobe 900′ is generating a plasma within the disc. If it is determinedthat the Coblation® mechanism is not occurring, (e.g., due to aninsufficiency of electrically conductive fluid within the disc), thesurgeon can then replenish the supply of the electrically conductivefluid to the disc.

[0237]FIG. 42 is a side view of an electrosurgical probe 900′ includingshaft 902″ having tracking device 942 located at distal end portion902″a. Tracking device 942 may serve as a radiopaque marker adapted forguiding distal end portion 902″a within a disc. Shaft 902″ also includesat least one active electrode 910 disposed on the distal end portion902″a. Preferably, electrically insulating support member or collar 916is positioned proximal of active electrode 910 to insulate activeelectrode 910 from at least one return electrode 918. In mostembodiments, the return electrode 918 is positioned on the distal endportion of the shaft 902″ and proximal of the active electrode 910. Inother embodiments, however, return electrode 918 can be omitted fromshaft 902″, in which case at least one return electrode may be providedon ancillary device 940, or the return electrode may be positioned onthe patient's body, as a dispersive pad (not shown).

[0238] Although active electrode 910 is shown in FIG. 42 as comprising asingle apical electrode, other numbers, arrangements, and shapes foractive electrode 910 are within the scope of the invention. For example,active electrode 910 can include a plurality of isolated electrodes in avariety of shapes. Active electrode 910 will usually have a smallerexposed surface area than return electrode 918, such that the currentdensity is much higher at active electrode 910 than at return electrode918. Preferably, return electrode 918 has a relatively large, smoothsurfaces extending around shaft 902″ in order to reduce currentdensities in the vicinity of return electrode 918, thereby minimizingdamage to non-target tissue.

[0239] While bipolar delivery of a high frequency energy is thepreferred method of debulking the nucleus pulposus, it should beappreciated that other energy sources (i.e., resistive, or the like) canbe used, and the energy can be delivered with other methods (i.e.,monopolar, conductive, or the like) to debulk the nucleus.

[0240]FIG. 43A shows a steerable electrosurgical probe 950 including ashaft 952, according to another embodiment of the invention. Preferably,shaft 952 is flexible and may assume a substantially linearconfiguration as shown. Probe 950 includes handle 904, shaft distal end952 a, active electrode 910, insulating collar 916, and return electrode918. As can be seen in FIG. 43B, under certain circumstances, e.g., uponapplication of a force to shaft 952 during guiding or steering probe 950during a procedure, shaft distal end 952 a can adopt a non-linearconfiguration, designated 952′a. The deformable nature of shaft distalend 952′a allows active electrode 910 to be guided to a specific targetsite within a disc.

[0241]FIG. 44 shows steerable electrosurgical probe 950 inserted withinthe nucleus pulposus of an intervertebral disc. An ancillary device 940and ancillary introducer 928 may also be inserted within the nucleuspulposus of the same disc. To facilitate the debulking of the nucleuspulposus adjacent to a contained herniation, shaft 952 (FIG. 43A) can bemanipulated to a non-linear configuration, represented as 952′.Preferably, shaft 955/952′ is flexible over at least shaft distal end952 a so as to allow steering of active electrode 910 to a positionadjacent to the targeted disc abnormality. The flexible shaft may becombined with a sliding outer shield, a sliding outer introducer needle,pull wires, shape memory actuators, and other known mechanisms (notshown) for effecting selective deflection of distal end 952 a tofacilitate positioning of active electrode 910 within a disc. Thus, itcan be seen that the embodiment of FIG. 44 may be used for the targetedtreatment of annular fissures, or any other disc abnormality in whichCoblation® is indicated.

[0242] In one embodiment shaft 952 has a suitable diameter and length toallow the surgeon to reach the target disc or vertebra by introducingthe shaft through the thoracic cavity, the abdomen or the like. Thus,shaft 952 may have a length in the range of from about 5.0 cm to 30.0cm, and a diameter in the range of about 0.2 mm to about 20 mm.Alternatively, shaft 952 may be delivered percutaneously in a posteriorlateral approach. Regardless of the approach, shaft 952 may beintroduced via a rigid or flexible endoscope. In addition, it should benoted that the methods described with reference to FIGS. 41 and 44 mayalso be performed in the absence of ancillary introducer 938 andancillary device 940.

[0243] Although the invention has been described primarily with respectto electrosurgical treatment of intervertebral discs, it is to beunderstood that the methods and apparatus of the invention are alsoapplicable to the treatment of other tissues, organs, and bodilystructures. For example, the principle of the “S-curve” configuration ofthe invention may be applied to any medical system or apparatus in whicha medical instrument is passed within an introducer device, wherein itis desired that the distal end of the medical instrument does notcontact or impinge upon the introducer device as the instrument isadvanced from or retracted within the introducer device. The introducerdevice may be any apparatus through which a medical instrument ispassed. Such a medical system or apparatus may include, for example, acatheter, a cannula, an endoscope, and the like. Thus, while theexemplary embodiments of the present invention have been described indetail, by way of example and for clarity of understanding, a variety ofchanges, adaptations, and modifications will be obvious to those ofskill in the art. Therefore, the scope of the present invention islimited solely by the appended claims.

What is claimed is:
 1. A method of using an electrosurgical system fortreatment of a contained herniation of an intervertebral disc of apatient, the electrosurgical system including a power supply unitfunctionally coupled to at least one active electrode, the at least oneactive electrode disposed on a shaft distal end of an electrosurgicalprobe, and the method comprising: a) guiding the shaft distal end withinthe intervertebral disc such that the at least one active electrode isin the vicinity of the contained herniation; and b) applying a highfrequency voltage between the at least one active electrode and at leastone return electrode, wherein at least a portion of tissue in thevicinity of the contained herniation is ablated.
 2. The method of claim1, further comprising, before said step a): c) advancing an introducerneedle towards the intervertebral disc, the introducer needle includinga lumen and a needle distal end; d) passing the shaft distal end throughthe lumen distally beyond the needle distal end, wherein the at leastone active electrode avoids contact with the needle distal end; and e)retracting the shaft distal end into the lumen of the introducer needle,wherein the at least one active electrode avoids contact with the needledistal end.
 3. The method of claim 1, wherein the at least one returnelectrode is located on the shaft or on a dispersive pad.
 4. The methodof claim 1, wherein the contained herniation comprises a bulge in anucleus pulposus of the disc and the bulge in the nucleus pulposus iscontained within an annulus fibrosus of the disc.
 5. The method of claim1 , wherein said step b) results in molecular dissociation of disctissue in the vicinity of the contained herniation, and the volume ofthe nucleus pulposus is decreased.
 6. The method of claim 2, wherein theguiding step is performed after the shaft distal end has been extendeddistally beyond the needle distal end.
 7. The method of claim 1, whereinthe guiding step comprises rotating the shaft about its longitudinalaxis.
 8. The method of claim 7, wherein the guiding step furthercomprises axial translation of the shaft.
 9. The method of claim 1,wherein the shaft has a pre-defined curvature both prior to and aftersaid guiding step.
 10. The method of claim 1, wherein the method isperformed percutaneously.
 11. The method of claim 1, wherein said stepa) is performed under fluoroscopy, and the position of the shaft distalend relative to the contained herniation is visualized fluoroscopically.12. The method of claim 11, wherein the shaft includes a radiopaquetracking device on the shaft distal end, or at least one radiopaquedepth marking.
 13. The method of claim 9, wherein the pre-definedcurvature comprises a first curve and a second curve proximal to thefirst curve, and the first curve and the second curve are in the sameplane relative to the longitudinal axis of the shaft.
 14. The method ofclaim 13, wherein the first curve is characterized by a first angle andthe second curve is characterized by a second angle, wherein the firstangle is in the range of from about 2° to about 8°, and the second angleis in the range of from about 4° to about 18°.
 15. The method of claim1, wherein the at least one active electrode comprises an electrode headhaving a substantially apical spike and a substantially equatorial cusp,and the apical spike and the equatorial cusp provide a high currentdensity in the vicinity of the electrode head upon application of thehigh frequency voltage between the at least one active electrode and thereturn electrode, the high current density promotes formation of aplasma in the vicinity of the electrode head, and the plasma causeslocalized ablation of disc tissue at a temperature in the range of fromabout 45° C. to about 90° C.
 16. The method of claim 1, wherein the disccomprises a fragment of nucleus pulposus.
 17. The method of claim 1,wherein the method is performed in conjunction with epidural injectionof a steroid.
 18. A method of ablating tissue at a target site of anintervertebral disc having a contained herniation, the methodcomprising: a) providing an electrosurgical system including a probe, anintroducer needle, and a power supply unit coupled to the probe, theprobe having a shaft, the shaft including a distal end portion having atleast one active electrode, the introducer needle having a lumen foraccommodating axial movement of the shaft therein; b) advancing theintroducer needle towards the intervertebral disc; c) passing the shaftdistal end portion distally through the lumen of the introducer needletowards the disc, wherein the shaft distal end portion is positioned inthe vicinity of the contained herniation; and d) applying a highfrequency voltage between the at least one active electrode and at leastone return electrode, the high frequency voltage selected for ablatingdisc tissue at the target site.
 19. The method of claim 18, wherein thetarget site comprises a bulge in a nucleus pulposus, the bulge in thenucleus pulposus is contained within an annulus fibrosus, and the methodfurther comprises: e) guiding the shaft distal end portion to the bulgein the nucleus pulposus.
 20. The method of claim 19, wherein the shaftdistal end portion has a pre-defined curvature, and said step e)comprises: f) during said step c), rotating the shaft about itslongitudinal axis.
 21. The method of claim 18, wherein the method isperformed percutaneously under fluoroscopy, and the position of theshaft distal end portion relative to the target site is visualizedfluoroscopically.
 22. The method of claim 18, wherein said step d)results in ablation of disc tissue, the volume or the mass of the disctissue is decreased, and discogenic pain is alleviated.
 23. The methodof claim 18, wherein said step d) comprises applying a high frequencyvoltage in the range of from about 150 volts rms to about 350 volts rmsbetween the at least one active electrode and the at least one returnelectrode, such that disc tissue at the target site is ablated at atemperature in the range of from about 45° C. to about 90° C.
 24. Themethod of claim 18, further comprising: h) applying a quantity of anelectrically conductive fluid in the vicinity of the at least one activeelectrode.
 25. The method of claim 18, wherein the shaft includes afirst curve and a second curve proximal to the first curve, and thefirst curve and the second curve are in the same plane relative to thelongitudinal axis of the shaft
 26. The method of claim 18, wherein theat least one active electrode includes a filament, the shaft includes afirst insulating sleeve encasing the filament, a return electrode on thefirst insulating sleeve, an insulating collar located at a distal end ofthe first insulating sleeve proximal to the return electrode, a secondinsulating sleeve on the return electrode, and a shield on the secondinsulating sleeve.
 27. The method of claim 18, wherein the at least oneactive electrode comprises an electrode head having a substantiallyapical spike and a substantially equatorial cusp, and the apical spikeand the equatorial cusp provide a high current density in the vicinityof the electrode head upon execution of said step d).
 28. The method ofclaim 18, further comprising the step of: l) injecting a steroid into anepidural space adjacent to the intervertebral disc.